Appendix B. Notes on Individual Galaxies

 

Based on the 1D radial profiles and 2D spectral maps, we describe important features of individual galaxies. We also include the distinct features previously known by targeted studies. We use the terms, SB (surface brightness), T (temperature), EM (emission measure), P (projected or pseudo pressure) and K (projected or pseudo entropy). In describing temperature profiles, we call the case with a negative T gradient in the central region (roughly within a few kpc or ~0.5 re) a hot core and the case with a positive T gradient in the central region a cool core.

 

IC 1262 (d=130.0 Mpc,  1' =  37.8 kpc,  re=  7.7 kpc,  r25= 22.7 kpc)  

It is a dominant galaxy in a small group. While the hot gas halo is roughly symmetric and smooth on a large scale (> 100 kpc), the hot ISM on a smaller scale exhibits rather complex substructures: a sharp discontinuity to the E and narrow arcs over 100 kpc long to the NS direction (Trinchieri et al. 2007). Also detected are cavities at 10-20 kpc to the N (Dong et al 2010). The hot gas in the enhanced surface brightness regions to the E from the center in r < 20kpc (~1 keV) and to the NS in r =20-100 kpc (~1.2 keV) is cooler than the surrounding gas (~1.6 keV). The gas thermal structures are also visible in the entropy map: the lowest entropy gas is extended to the E, the lower entropy gas is extended to the NS, surrounded by the higher entropy gas.

 

IC 1459 (d= 29.2 Mpc,  1' =   8.5 kpc,  re=  5.2 kpc,  r25= 22.3 kpc)

It is a dominant galaxy in a small group. A strong nuclear source (LX = 8 x 1040 erg s-1) dominates the X-ray emission (Fabbiano et al. 2003). Because of the strong central source, there are (weak) ACIS readout streaks along the CCD column, visible in the smoothed diffuse image. Note that they are not excluded in this image, however, the streak regions were excluded in the spectral analysis (see section 4.3). The faint diffuse gas is extended to fill the D25 ellipse. While the surface brightness is azimuthally symmetric, the 2D temperatures map shows slight asymmetry in that the gas along the minor axis (0.6-0.7 keV) is hotter than that along the major axis (0.4-0.5 keV).

 

IC 1860 (d= 93.8 Mpc,  1' =  27.3 kpc,  re=  8.4 kpc,  r25= 23.7 kpc)

It is the BCG (brightest cluster galaxy) of Abell S301. It is previously known to be sloshing (Gastadello et al 2013). The intensity and temperature maps show a narrow tail, extending to r = 1 (or 27 kpc) toward the SE direction from the core. The gas in the tail is cooler (~1 kev) than that in the surrounding region (1.3 keV). The tail is also visible in the projected entropy map, but not obviously clear in the projected pressure map, indicating the pressure balance with the surrounding medium. Excluding the tail, the hot gas emission on a large scale (at or outside the D25 ellipse) is more pronounced toward the SW and relatively weaker toward the NE direction.

 

IC 4296 (d= 50.8 Mpc,  1' =  14.8 kpc,  re= 11.9 kpc,  r25= 25.0 kpc)

It is the BCG in Abell 3565. A strong nuclear source (LX = 2.4 x 1041 erg s-1) dominates the X-ray emission (Pellegrini et al. 2003; Humphrey & Buote 2006). The hot gas distribution is asymmetric, mainly extending to r = 1.6' or 20 kpc toward the SW direction in a fan-shape (PA=280-350°). The gas temperature in that region is hotter (~1.3 keV) than that in the central region (0.8 keV). The ACIS observation was done in a sub-array mode with 512 rows, but the entire D25 ellipse is included.  A nearby spiral galaxy, IC 4299 which is at 6.2' to the S of IC 4296 is also detected just inside the fov.

 

NGC 193 (d= 47.0 Mpc,  1' =  13.7 kpc,  re=  4.4 kpc,  r25=  9.9 kpc)

It is a FR-I radio galaxy (Laing et al. 2011). The hot gas exhibits a well-structured shell at r = 1′ - 1.5 (or 14-20 kpc). The radio lobes have inflated into a cocoon or a large cavity and the shell of shocked material around the cavity (Bogdan et al. 2014).  The gas in the cavity is cooler (~0.7 keV) than that in the shell (~ 1 keV).  It also has a distinct X-ray point source at the center. 

 

NGC 315 (d= 69.8 Mpc,  1' =  20.3 kpc,  re= 12.5 kpc,  r25= 32.9 kpc)

It is a FR-I radio galaxy. The Chandra observations reveal a strong nuclear X-ray source (LX = 5 x 1041 erg s-1) and also an X-ray jet (ΓPH ~ 2.2) extending to r = 1 (or 20 kpc), coincident with a NW radio jet (Worrall et al. 2003, 2007). The strong nucleus causes (weak) CCD readout streaks along the CCD column, which are visible in the diffuse image. Note that they are not excluded in this image, however, the streak regions were excluded in the spectral analysis (see section 4.3).

 

NGC 383 (d= 63.4 Mpc,  1' =  18.4 kpc,  re=  6.3 kpc,  r25= 14.6 kpc)

It is a FR-I radio galaxy (3C 31). The Chandra observations reveal a strong nuclear X-ray source (several x 1041 erg s-1) and also an X-ray jet extending to r = 10′′ or 3 kpc, coincident with brighter, northern radio jet of 3C 31 (Hardcastle, et al. 2002). Because of its small scale, the northern jet is only seen in the unsmoothed image. A nearby galaxy, NGC 382, lying inside the D25 ellipse at ~0.6 S (PA=200°) from NGC 383 is also detected with a similar gas temperature (~0.7 keV). A few nearby galaxies of the Arp 331 chain (see the table below) are also detected in the ACIS fov.

 

-----------------------------------------------------

 name       RA          DEC         D(′)      PA(deg)

          (J2000)      (J2000)   from N383  from N383

-----------------------------------------------------

 NGC 375  16.77466     32.34817     5.6′      226

 NGC 379  16.81537     32.52036     6.8′      343

 NGC 380  16.82330     32.48292     4.5′      340

 NGC 382  16.84946     32.40386     0.6’      200

 NGC 384  16.85460     32.29245     7.2′      180

 NGC 385  16.86352     32.31953     5.6′      175

 NGC 386  16.88039     32.36199     3.3′      156

 NGC 387  16.88775     32.39111     2.2′      127

-----------------------------------------------------

 

NGC 499 (d=54.45 Mpc, 1=15.8 kpc,  re=4.4 kpc,  r25 =12.8 kpc )

It is the 2nd brightest galaxy in the NGC 507 group (13.7to the NW, PA=334° from NGC 507). Given its high LX,GAS (> 1042 erg s-1) and TGAS (~ 1 keV at the outskirts), it is likely a separate group which is currently merging with the NGC 507 group. NGC 499 and NGC 507 belong to one group in the 2MASS group catalog (Crook et al. 2007), but they are identified as two separate groups in Lyon group catalog (Garcia 1993). The temperature radial profile is a typical case with a hot core. In contrast to a cool core, the T gradient is negative in the inner region (r < 10 kpc) and positive in the outer region (r > 10 kpc). Although at the outskirts (r > 70 kpc) the temperature (as well as the surface brightness) goes up with increasing radius due to the hotter ICM of the NGC 507 group, the inner temperature profile is not affected by the ICM and therefore intrinsic to NGC 499. The 2D temperature map further shows that the gas distribution is azimuthally asymmetric. The inner hotter gas (~0.85 keV) extending to r = 20′′ or 5 kpc is elongated along the major axis (PA = 70°) while the outer cooler gas (~0.65 keV) extending to r = 2or 30 kpc is elongated along the NE-SW direction (PA ~ 40°). There are two possible ghost cavities just outside the D25 ellipse (at r =10-15 kpc), one to the N (PA ~ 20°) and another to the S (PA ~ 160°) from the galaxy center, seen in the diffuse image as well as in the projected pressure map. It is likely that all these features suggest the past, multiple AGN activities.

 

NGC 507 (d=63.8 Mpc, 1=18.6 kpc,  re=12.9 kpc,  r25 =28.7 kpc )

It is the BCG in an optically rich group, merging with NGC 499 (at 13.7 to the NW, PA=334). The T profile indicates the presence of a cool core and the SB profile shows the central cusp. The 2D maps illustrate rather complex substructures. Its core region has cavities, possibly related to the old bent radio lobes (Giacintucci et al 2011). Kraft et al. (2004) identified an abundance front. The hot gas is probably sloshing owing to interaction with NGC 499.  NGC 508 at ~1.5 to the N is also detected in the same observation.

 

NGC 533 (d=76.9 Mpc, 1= 22.4 kpc,  re=16.2 kpc,  r25=42.5 kpc)

It is a relaxed group with a cool core (Eckmiller et al. 2011; Panagoulia et al. 2014). The T profile shows cooler gas (T ~ 0.8 keV) in the inner region (r < 5 kpc). The temperature steeply rises to ~1.3 keV at r = 16 kpc (close to re), then remains constant to r = 80 kpc (~5 re). The T map further indicates an asymmetric cool core. Inside r = 20 kpc, the hot gas is distributed along the major axis, generally following the optical light distribution (ellipticity e = 0.4). This is most clearly seen in the T and projected entropy maps, possibly indicating sloshing by a nearby galaxy. In the outer region (r = 20-60 kpc), the hot gas is more extended to the N and NE than toward the S. Note that the lower SB region just inside the D25 ellipse to the S is affected by the node boundary which is not fully corrected even in the exposure corrected diffuse emission map. However, the lower SB region outside the D25 ellipse toward the S is not affected. Shin et al. (2016) found two cavities at 1.5 kpc N and S of the nucleus. There is a possible ghost cavity at r~5 kpc from the center toward the NW.

 

NGC 720 (d=27.7 Mpc,  1 = 8.0 kpc,  re=4.8 kpc,  r25=18.8 kpc)

It was extensively studied as a relaxed system where mass can be measured accurately (Buote et al. 2002 and Humphrey et al. 2011). Both T profile and T map show more or less constant T (~0.6 keV) throughout the galaxy (r = 2 - 20 kpc) with hints of increasing T toward the center and decreasing T at the outskirts. Unlike NGC 533, the gas distribution is considerably rounder than the optical figure (e = 0.5), as seen in the intensity map as well as the projected pressure and entropy maps.

 

NGC 741 (d=70.9 Mpc,  1 = 20.6 kpc,  re=13.2 kpc,  r25=30.4 kpc)

It is a disturbed system, owing to a NAT radio galaxy (PKS 0153+05) and NGC 742 (at 0.8 to the E) falling through the core. Jetha et al (2008) reported complex gas structures with X-ray filaments linking NGC 741 and NGC 742 and a possible ghost cavity to the W of NGC 741 (see also Schellenberger et al. 2017). Even if it is not relaxed, NGC 741 has a cool core (~0.7 keV) and hotter gas (1.2 keV) at the outskirts. NGC 742 has a nuclear X-ray source at the center which dominates its entire X-ray emission. Also detected in the ACIS field of view are two compact galaxies, ARK065 and ARK066, at the similar redshift with NGC 741 and 742.

 

------------------------------------------------------------------------

 name       RA          DEC         D(′)      PA(deg)       other

          (J2000)      (J2000)   from N741  from N741       names

------------------------------------------------------------------------

 NGC 742  29.10072     5.62668      0.8′      100

 ARK065   29.05004     5.58858      3.3′      223       P007237 

 ARK066   29.07938     5.65208      1.5′      341       P007250  IC 1751

------------------------------------------------------------------------

 

NGC 1052 (d=19.4 Mpc,  1 = 5.6 kpc,  re=3.1 kpc,  r25=8.5 kpc)

It is a well-known LINER. A variable nuclear X-ray source dominates the entire X-ray emission (Hernández-García et al. (2013). Soft (0.4 keV) diffuse gas emission is seen inside a few kpc from the center. Asymmetric T maps (0.4 keV to the E and 0.7 keV to the W) seen in WB and HB need to be confirmed by deeper observations.

 

NGC 1132 (d=95.0 Mpc,  1 = 27.6 kpc,  re=15.5 kpc,  r25=34.7 kpc)

It is a fossil group with an extended, luminous X-ray halo (LX ~ 7 x 1042 erg s-1, Lovisari et al. 2015). The T profile shows a cool core (~0.8 keV). The azimuthally average temperature peaks at ~10 kpc (1.3 keV) and declines outwards to ~1 keV. In contrast to the expectation as a fossil system, the hot gas morphology indicates asymmetry, an edge to the E and extended emission to the W, possibly implying a rare case of a rejuvenated fossil group (e.g., von Benda- Beckmann et al. 2008). The detail observational results and implications are presented in a separate paper (Kim et al., 2018).

 

NGC 1316 (d=21.5 Mpc,  1 = 6.2 kpc,  re=7.6 kpc,  r25=37.6 kpc)

It is a radio galaxy (Fornax A) with radio jets and extended lobes to the E-W direction (Ekers et al. 1983) and exhibits a number of signs for recent major mergers in 2-3 Gyr ago (Schweizer 1980). The hot gas morphology also indicates disturbed nature and cavities associated with the radio jets (Kim & Fabbiano 2003). Given the large optical luminosity and size of the stellar system, the amount (LX,GAS ~ a few x 1040 erg s-1) and the extent (~10 kpc) of hot gas are very low, making its LX/LK one of the lowest for among nearby ETGs. The azimuthally averaged temperature decreases from the center to r ~ 10 kpc, then increases outwards to 20 kpc. But the SB and temperature maps indicate the gas is not symmetric.

 

NGC 1332 (d=22.9 Mpc,  1 = 6.7 kpc,  re=3.1 kpc,  r25=15.6 kpc)

It is an edge-on S0 galaxy. The temperature is almost constant at 0.6 keV inside the D25 ellipse, except that the hot gas may be slightly hotter (~0.7 keV) in the central region.

 

NGC 1380 (d=17.6 Mpc,  1 = 5.1 kpc,  re=3.2 kpc,  r25=12.3 kpc)

It is an edge-on S0 galaxy in the Fornax cluster. It is located at 37.8to the NW from NGC 1399. The hot ISM (~0.3 keV) is detected but confined within a few kpc (~1 re). The hotter (1.2-1.5 keV) ICM in the Fornax cluster is also detected at r > 10 kpc.

 

NGC 1387 (d=20.3 Mpc,  1 = 5.9 kpc,  re=3.5 kpc,  r25=8.3 kpc)

It is a barred S0 (SB0) galaxy in the Fornax cluster. It is located at 19to the W (PA=260) from NGC 1399. The hot ISM (~0.5 keV) is detected but confined within several kpc (or ~2 re). The hotter (1.2-1.5 keV) ICM in the Fornax cluster is also detected at r > 10 kpc. Note that the X-ray bright part is on the ACIS-I chip gap, although the exposure map appears to work properly.

 

NGC 1395 (d=24.1 Mpc, 1 = 7.0 kpc,  re=5.4 kpc,  r25=20.6 kpc)

It is a large elliptical galaxy (MK = -25 mag), and the hot gas temperature is comparably high (0.8 - 0.9 keV). Given the short Chandra observations with significant background flares, the hot gas is limited roughly within the D25 ellipse, and its temperature is more or less constant.

 

NGC 1399 (d=20.0 Mpc,  1 = 5.8 kpc,  re=4.7 kpc,  r25=20.1 kpc)

It is at the center of the Fornax cluster and contains a large amount of extended hot halo. Although NGC 1316 (3.6° away in projection) is optically brighter by a factor of two (hence BGC), NGC 1399 is at the bottom of the potential well. On a galaxy scale (inside the D25 ellipse), the intensity maps show two filaments to the north and one to the south. The radio jets are propagating between the two northern filaments and at the side along the southern filament (Paolillo et al. 2002 and Werner et al. 2012). The T maps show the cooler gas (0.8-1 keV) extending to the N-S direction along the filaments. The projected pressure map also shows the gaps where the radio jets are propagating. On a large cluster scale, the Chandra observations of the Fornax cluster (3x3 ACIS-I observations) reveal the asymmetric intracluster gas (Scharf et al. 2005). The hot halo is extended to r ~30 (180 kpc) to the NE of NGC 1399. A few discontinuities, likely due to sloshing, are also detected by Su et al. (2017b).

 

NGC 1400 (d=26.4 Mpc,  1 = 7.7 kpc,  re=2.9 kpc,  r25=8.8 kpc)

It is a member of the NGC 1407 / NGC 1400 merging group, 12away to the SW (PA=236°) from NGC 1407. Note that the galaxy (the NW side) is not fully covered by the deeper one of two observations. The hot ISM (0.5-0.6 keV) is confined inside the D25 ellipse and surrounded by the hotter ambient gas (~1.2 keV) at r > 20 kpc. There is also a blob of hot gas at 3-5 away to the NE from NGC 1400 (Giacintucci et al. 2012, Su et al. 2014). Because the external hot gas has a similar temperature and abundance to that of NGC 1400, Su et al. (2014) suggested that it might have come out of NGC 1400 by ram pressure stripping.

 

NGC 1404 (d=21.0 Mpc,  1 = 6.1 kpc,  re=2.7 kpc,  r25=10.1 kpc)

It is a member of the Fornax cluster, only 10 (in projection 60 kpc) away to the SE (PA=152°) from NGC 1399. It is one of the most extensively studied ETGs due to a sharp discontinuity to the direction of NGC 1399 (Machacek et al 2005, Su et al. 2017a). The Chandra observations reveal a front at the NW edge and a tail to the SE, indicating that it is currently falling through the Fornax cluster. The temperature radial profile indicates a hot core as in the case of NGC 499. The temperature is 0.8 keV at the central region and decreases to 0.5 keV at r = 4 kpc (just outside re) and steeply rise at r=5-20 kpc to 1.3 keV. In the 2D spectral maps, the head-tail structure is clearly visible.

 

NGC 1407 (d=28.8 Mpc,  1 = 8.4 kpc,  re=8.9 kpc,  r25=19.2 kpc)

It is the BCG in a small group. It has a cool core with an edge to the N (at r =7-8 kpc) and wings extending to the E-W, suggesting that the galaxy is moving to the N direction. The wings are inside

a large scale, old diffuse radio structure, and they are bent likely as a consequence of motion to the N (Giacintucci et al, 2012). The temperature radial profile indicates another hot core case: T is ~ 1 keV in the center, decreases to ~0.8 keV at r = 1-3 kpc, then rises to ~1.3 keV at the outskirts (r > 20 kpc). The temperature maps further reveal the cooler E-W wings extending beyond the D25 ellipse.

 

NGC 1550 (d=51.1 Mpc,  1 = 14.9 kpc,  re=6.3 kpc,  r25=16.6 kpc)

It is a dominant galaxy in a group. This group is one of the most luminous local groups with LX ~ 1043 ergs s-1 within 200 kpc (Sun et al. 2003). On a large scale, the hot gaseous halo is smooth and circularly symmetric as seen in the XMM-Newton observations (Kawaharada et al. 2009) but the central region is highly elongated. The 2D temperature map further suggests an asymmetric distribution of cooler gas (~1 keV) with a strong E-W elongation, being more pronounced to the W. A similar trend is also seen in the projected entropy map while it is not seen in the projected pressure map, indicating pressure balance between the cooler/low entropy and hotter/high entropy gas. The temperature radial profile shows that the temperature is constant at ~1 keV within r < 5 kpc and rises to ~1.5 keV at r ~ 30 kpc, then declines at the outskirts. Note that the CCD boundary of one of the two long ACIS-S observations falls at the southern end of the D25 ellipse. While the boundary is clearly visible in the raw and binned images, it is properly treated in spectral fitting so that the spectral maps are smooth across the boundary.

 

NGC 1553 (d=18.5 Mpc,  1 = 5.4 kpc,  re=5.1 kpc,  r25=12.0 kpc)

It is a face-on SB0 galaxy. A hard X-ray source (LX ~ 1040 erg s-1) is present at the nucleus and the diffuse hot gas (~0.4 keV) roughly fills the D25 ellipse. The gas emission is not smooth, the SB radial profile is rather flat and spiral arm like features starting from the center are seen along the minor axis (see also Blanton et al 2001). A deeper observation is necessary to confirm the distribution and its thermal structure of the hot gas.

 

NGC 1600 (d=57.4 Mpc,  1 = 16.7 kpc,  re=13.5 kpc,  r25=20.5 kpc)

It is either a BCG in a loose group or an isolated elliptical galaxy surrounded by a number of satellite galaxies (Smith et al. 2008). Due to its low X-ray luminosity (a few x 1041 erg s-1), it is not identified as a fossil group. It hosts a massive BH of 1.7 x 1010 M¤ (Thomas et al. 2016). The temperature profile is a typical one with a cool core. The cool core is at T ~ 0.8 keV and T reaches a peak (T ~ 1.5 keV) at a few re, then declines outward. Also detected in X-rays are NGC 1603 (2.5 E of NGC 1600) and NGC 1601 (1.6 N of NGC 1600). The hot gas in NGC 1603 shows a tail to the W, due to the ram pressure from the group halo as the galaxy is moving to the E (Sivakoff et al. 2004). There is no clear signature of sloshing in the main halo, likely because NGC 1603 is too small to perturb the hot halo of the main galaxy as DmB = 2.7.  

 

NGC 1700 (d=44.3 Mpc,  1 = 12.9 kpc,  re=3.86 kpc,  r25=21.4 kpc)

It is a giant (MK=-25.5) elliptical galaxy. A hard X-ray source (LX ~ a few x 1040 erg s-1) is present at the nucleus and the diffuse hot gas (~0.5 keV) roughly fills the D25 ellipse. The hot gas distribution is significantly flattened likely due to the rotation, consistent with the stellar figure (E4) and kinematics (Statler & McNamara 2002). The temperature radial profile indicates a mild negative gradient (from 0.55 to 0.35 keV).

 

NGC 2300 (d=30.4 Mpc,  1 = 8.8 kpc,  re=4.8 kpc,  r25=12.5 kpc)

It is the BCG in a group with neighboring stripped spiral galaxy NGC 2276 which is moving to the SW at ~850 km s-1 and both galaxies are detected in X-rays (Rasmusen et al 2006). The temperature profile of NGC 2300 is a typical one with a cool core. The cool core is at ~0.6 keV and T reaches a peak ~1 keV at a few re, then declines outward. There may an edge to the E and NE and the diffuse gas is more extended to the SW. This may be due to sloshing by NGC 2276 (6 away) after it has just passed the impact point.

 

NGC 2563 (d=67.8 Mpc,  1 = 19.7 kpc,  re=6.4 kpc,  r25=20.6 kpc)

It is a dominant galaxy in a poor group with a typical cool core. The temperature is 0.8 keV near the center, peaks (T ~ 1.7 keV) at r=20 kpc (3 re), then declines outward. A nearby SB0 galaxy, NGC 2557 is also detected in X-rays. Rasmussen et al. (2012) studied individual group members with hot (X-rays) and cold (HI) gas to investigate the effect of ram pressure stripping and tidal interactions.

 

NGC 3115 (d=9.7 Mpc,  1= 2.8 kpc,  re=1.6 kpc,  r25=10.2 kpc)

An edge-on S0 galaxy with little hot gas. It is one of the gas poor ETGs with very deep Chandra observation, targeted to study the Bondi accretion (Wong et al. 2014; Lin et al. 2015a, b). The hot gas is detected within ~1 re.

 

NGC 3379 (d=10.6 Mpc,  1 = 3.1 kpc,  re=2.4 kpc,  r25=8.3 kpc)

It is a typical old E galaxy with little hot gas. It is one of the gas poor ETGs with very deep Chandra observations, targeted to study a population of LMXBs (Brassington et al. 2008, 2010). The hot gas (T~0.3 keV) is detected within ~1 re and its luminosity is one of the lowest ever measured from a hot phase of the ISM among genuine elliptical galaxies, as likely in the outflow phase (Trinchieri et al 2008).

 

NGC 3402 = NGC 3411 (d=64.9 Mpc,  1 = 18.9 kpc,  re=8.8 kpc,  r25=19.7 kpc)

It is the BCG in a small group, USGC S152. While the diffuse gas appears to be relaxed, the temperature map clearly indicates a shell-like structure at 20-40 kpc with cooler gas (~0.8 keV) surrounded by inner and outer hotter gas (~1 keV), as previously reported by O’Sullivan et al. (2007). The cooler gas is most obvious to the N (PA=-20 – 20°) and E (PA = 90-135°) and least to the SW (PA = 220-300°). This feature is not seen in the intensity, EM, projected pressure and projected entropy maps. It is not understood what caused the cooler shell. The possibilities include a previous AGN activity which could reheat the cool core and settling of material stripped from the halo of one of the other group member galaxies (O’Sullivan et al. 2007).

 

NGC 3607 (d=22.8 Mpc,  1 = 6.6 kpc,  re=5.0 kpc,  r25=16.2 kpc)

It is a dominant E/S0 galaxy in a small group USGC U376 in the Leo cloud (Mazzei et al. 2014) with NGC 3608 (5.9 N) and NGC 3605 (2.7 SW). A hot core (~1 keV) may be present in the central region (r < 0.5 kpc) and then the gas temperature remains constant at 0.5 keV in r < re. The SB profile is also relatively flat (~r-1) at r =1-10 kpc. Given the limited statistics of the Chandra data, it is not clear whether the hot gas indicates any sign of interactions. Both NGC 3607 and 3608 are known to be a LINER and the X-ray nuclear sources were studied by Flohic et al. (2006).

 

NGC 3608 (d=22.9 Mpc,  1 =  6.7 kpc,  re=3.3 kpc,  r25=10.5 kpc)

It is an elliptical galaxy at 5.9 (or ~40 kpc in projection) away from NGC 3607 and in the same fov of the Chandra observation of NGC 3607. As it is slightly smaller than NGC 3607 (0.8 mag less bright in K-band), its LX and TX are slightly smaller. The gas temperature is constant ~0.4 keV and the SB profile is relatively flat (~r-1) at r < 2 re.

 

NGC 3842 (d=97.0 Mpc,  1 = 28.2 kpc,  re=17.8 kpc,  r25=19.9 kpc)               

It is the BCG of Abell 1367, but it is not at the center of the hot ICM, nor at the center of the cluster potential well. The diffuse hot gas at T ~ 1 keV is detected inside the D25 ellipse. The hot ISM is embedded inside the hotter (5-6 keV) subcluster which is merging with the primary cluster of Abell 1367 centered at 20’ SE of NGC 3842 (see Sun et al. 2005a, b).  A few other galaxies in Abell 1367 subcluster (see the table below) are also detected in the same fov.

 

-------------------------------------------------------------------------------

 name       RA          DEC         D(′)      PA(deg)       Notes

          (J2000)      (J2000)   from N3842  from N3842    

-------------------------------------------------------------------------------

 N3841    176.00896   19.97189      1.33       0.5       E

 N3837    175.98511   19.89458      3.57       202       E

 P169975  175.98833   19.95500      1.19       285       S0 CGCG 097090

 U06697   175.95446   19.96844      3.26       290       starburst CGCG 097087

 QSO      175.98706   19.94705      1.23       263       at z=0.35

--------------------------------------------------------------------------------

 

NGC 3923 (d=22.9 Mpc,  1 = 6.7 kpc,  re=5.8 kpc,  r25=19.6 kpc)

It is a young elliptical (E4) galaxy with a number of stellar shells (Bilek et al. 2016).  The extended hot gas is detected inside the D25 ellipse and is elongated along the major axis, but not as flat as the stellar system. In the inner region, the temperature decreases with increasing r, i.e., a hot core (0.7 keV at r=0.1 kpc). T reaches at the minimum (0.4 keV) at r=3kpc, then increases again to 0.6 keV at r=10-20 kpc. Kim & Fabbiano (2010) and Kim et al. (2012) investigated this galaxy among a sample of young elliptical galaxies, in terms of the X-ray binary luminosity function and the hot gas metallicity.

 

NGC 4104 (d=120.0 Mpc,  1 = 34.9 kpc,  re=20.0 kpc,  r25=44.9 kpc)

It is a dominant galaxy in a small group. Given the shallow Chandra observation of this distant galaxy, its 2D spatial features are not clearly visible. Its radial temperature profile shows a cool core (~ 1 keV inside a few kpc) and a temperature peak (~1.5 keV) at r=20-40 kpc.

 

NGC 4125 (d=23.9 Mpc,  1 = 6.9 kpc,  re=5.9 kpc,  r25=20.0 kpc)

It is a flattened elliptical (E6) galaxy. Similar to NGC 3923, the extended hot gas is detected inside the D25 ellipse and is elongated along the major axis, but not as flat as the stellar system. It hosts a hot core, as in NGC 3923. The temperature peaks at 0.6 keV at r=0.1 kpc and decreases with increasing r, reaching a minimum (~0.3 keV) at the outer boundary where the gas temperature can be measured (~30 kpc). It also shows the characteristics of young ellipticals in their X-ray binary luminosity function (Kim & Fabbiano 2010; Zhang et al. 2012).

 

NGC 4261 (d=31.6 Mpc,  1 = 9.2 kpc,  re=6.9 kpc,  r25=18.7 kpc)

It is a group dominant elliptical and also a FR-I radio galaxy (3C270). The bright AGN dominates the X-ray emission. The X-ray jets are detected at the position coincident with the radio jets and the compressed rims of the X-ray cavities are correlated with radio lobes (Zezas et al. 2005; Worrall et al. 2010; O'Sullivan et al 2011). The faint diffuse emission from the hot gas is detected inside the D25 ellipse. The temperature is constant at ~0.7 keV in the inner region (r = 0.1 - 2 kpc), then abruptly increases to 1.3 keV at r = 5 kpc and remains high to the maximum radius (~30 kpc).

 

NGC 4278 (d=16.1 Mpc,  1 = 4.7 kpc,  re=2.6 kpc,  r25=9.5 kpc)

It is one of the gas poor old elliptical galaxies. With deep Chandra observations (560 ksec), a population of LMXBs (Brassington et al. 2009; Fabbiano et al. 2010) and their connection to globular clusters (Kim et al. 2009; Fabbiano et al. 2010), and a central LINER activity in conjunction with optical and infrared data (Pellegrini et al. 2012) were extensively investigated. The hot gas is extended out to r ~ 5 kpc and the temperature is constant (~0.3 keV), but steeply increases to ~0.7 keV in the inner 0.3 kpc (see also Pellegrini et al 2012).

 

NGC 4291 (d=26.2 Mpc,  1 = 7.6 kpc,  re=2.0 kpc,  r25=7.3 kpc)

Similar to NGC 4342, it is one of a few elliptical galaxies with unusually high BH-bulge mass ratios (see Bogdan et al. 2012a). The hot gas is extended roughly along the major axis, beyond the D25 ellipse. It has a hot core with a negative T gradient to the minimum (0.4 keV) at r ~ 4 kpc (or 2 re), then a positive T gradient to ~0.8 keV at r ~ 10 kpc. The T map shows that the cooler gas may be extended more to the E than to the W.

 

NGC 4325 (d=110.0 Mpc,  1 = 32.0 kpc,  re=10.5 kpc,  r25=15.3 kpc)

It is a dominant elliptical galaxy in a small group. The hot gas is extended (beyond the ACIS fov) and symmetric on a large scale (outside the D25 ellipse), the core region is rather complex with a cool core and cavities (Russell et al. 2007; Lagana et al. 2015). The temperature is about 0.7 keV in the central region, increases to ~1.1 keV at r=35 kpc, then decreases outward. The T map further shows that the cooler gas inside the D25 ellipse is elongated along the N-S, roughly following the major axis.

 

NGC 4342 (d=16.5 Mpc,  1 = 4.8 kpc,  re=0.5 kpc,  r25=3.1 kpc)

It is one of a few elliptical galaxies with unusually high BH-bulge mass ratios (see Bogdan et al. 2012a).  In contrast to a nearby massive elliptical NGC 4365, 20 away (or 130 kpc in projection), it is optically faint but hot gas rich, hence associated with a large amount of dark matter (Bogdan et al. 2012b). Its LX,GAS/LK is the highest among local ETGs, making it an extreme opposite to NGC 1316 with the lowest LX,GAS/LK. The SB map shows a head-tail structure with a discontinuity to the NE (just outside the D25 ellipse) and a wide extended tail to the SW. The T map shows the extended tail is filled by cooler (0.6 keV) gas.

 

NGC 4374 (d=18.4 Mpc,  1 = 5.3 kpc,  re=5.5 kpc,  r25=17.3 kpc)

It is one of the extensively studied elliptical galaxies in the Virgo cluster, also known as M84. It is at 17to the SW (PA=258) from NGC 4406 (M86) and at 89 to the NW (PA=290) from the center of the Virgo cluster, NGC 4486 (M87). The hot gas exhibits many interesting features, including pronounced filaments and cavities in the central region (r < 10 kpc) which are associated with the radio jets (Finoguenov et al. 2008) and an extended tail to the SW from the galaxy center in r=10-30 kpc, likely due to the ram pressure (Randall et al. 2008). The T profile shows a hot core with a negative T gradient out to a T minimum (~0.6 keV) at r ~ 1 kpc, then a positive T gradient to a T maximum (~1.5 keV) at r~30 kpc. The T maps further show asymmetric, disturbed thermal structures, the cooler gas (~0.8 keV) filling the southern part of the D25 ellipse and the hotter gas (~1.2 keV) filling the extended tail to the SW.

 

NGC 4382 (d=18.5 Mpc,  1 = 5.4 kpc,  re=7.4 kpc,  r25=19.0 kpc)

It is a young S0 galaxy in the Virgo cluster, also known as M85. It contains a small amount of hot gas for its stellar luminosity (Sansom et al. 2006) and therefore it is often used to study LMXBs (Sivakoff et al. 2003). Within the limited statistics, the relatively cool (~0.4 keV) and smooth hot gas does not show a distinct feature.

 

NGC 4406 (d=17.1 Mpc,  1 =  5.0 kpc,  re=10.3 kpc,  r25=22.2 kpc)

It is one of the extensively studied elliptical galaxies in the Virgo cluster, also known as M86. It is at 17to the NE (PA=78) from NGC 4374 (M84) and at 75 to the NW (PA=296) from the center of the Virgo cluster, NGC 4486 (M87). Its X-ray luminosity is the 2nd largest (M87 being the most luminous) among the Virgo galaxies. The X-ray emission from the extended plume to the NW from the galaxy center is as bright as that of the main body (e.g., Rangarajan et al. 1995). Based on its negative radial velocity (−250 km s−1), it is moving supersonically in the Virgo cluster with few other galaxies in the group (e.g., NGC 4438) and the extended plume may be related to ram pressure stripping (e.g., Randall et al. 2008).

 

NGC 4438 (d=18.0 Mpc,  1 = 5.2 kpc,  re=5.0 kpc,  r25=22.3 kpc)

It is an S0 galaxy in the Virgo cluster, possibly belongs to the M86 group. It is at 23 to the E (PA=81) from NGC 4406 (M86) and at 58 to the NW (PA=310) from the center of the Virgo cluster, NGC 4486 (M87). In addition to the hot gas in the central region, multiple filaments are visible to r~10 kpc to the W and SW, which may be due to the interaction with a nearby galaxy, NGC 4435, which is at 4.4 to the NE (Machacek et al. 2004). Also detected are the extended Ha filaments between M86 and NGC 4438, suggesting the interaction between these two galaxies (Kenney et al. 2008).

 

NGC 4472 (d=16.3 Mpc,  1 = 4.7 kpc,  re=8.3 kpc,  r25=24.2 kpc)

It is one of the extensively studied hot gas rich elliptical galaxies in the Virgo cluster, at 4.4° to the S from the cluster center, also known as M49. Although it is not at the cluster center, it is brightest in the Virgo cluster. There are multiple cavities in the central region (r < 10 kpc), the contact discontinuity (a cold front) at ~20 kpc to the N and extended tails to the E as well as longer tails to the SW which are extended beyond the ACIS fov. These hot gas features are clearly indicating interactions with the radio jets and ICM in the Virgo cluster (e.g., see Biller et al. 2004; also see Kraft et al. 2011 for XMM-Newton data analysis.)

 

NGC 4477 (d=16.5 Mpc,  1 = 4.8 kpc,  re=3.5 kpc,  r25=9.1 kpc)

It is a SB0 galaxy in the Virgo cluster at 75.6 to the N (PA=351) from the center of the Virgo cluster, NGC 4486 (M87). It is also known as Seyfert 2 (Veron-Cetty & Veron 2006) and the X-ray nucleus is detected. The hot gas is relatively cold (0.3-0.4 keV) and confined within the D25 ellipse. The SB map shows asymmetry, more extended to the N and W (than to the S and E) and also shows a distinct spiral like features.  The Chandra observations were primarily obtained for a distant (z ~ 1) luminous cluster (Fassbender et al. 2011, Lerchster et al. 2011), XMMUJ1230+1339, which is at 3.7to the E from NGC 4477.

 

NGC 4526 (d=16.9 Mpc,  1 = 4.9 kpc,  re=3.3 kpc,  r25=17.8 kpc)

It is an S0 galaxy in the Virgo cluster. It is at 66 to the E (PA=106°) from NGC 4472 (M49) and at 4.8° to the S (PA=170°) from the center of the Virgo cluster, NGC 4486 (M87). A relatively strong X-ray point source is detected in the center, although it is not a known AGN. The hot gas is relatively weak and cold (0.3 keV) and confined inside 1 re.

 

NGC 4552 (d=15.4 Mpc, 1 = 4.5 kpc,  re=3.1 kpc,  r25=11.4 kpc)

It is a S0 (listed as E0 in RC3) galaxy in the Virgo cluster, at 72 to the E from the cluster center, also known as M89. The LINER nucleus source is detected in X-ray (Xu et al. 2005). In contrast to the relaxed old stellar system, the hot gas morphology shows an excellent example of the head-tail structure, likely caused by the relative motion inside the Virgo ICM, as it is falling into the cluster center (Machacek et al. 2006a, b). The cold front on the N has Kelvin–Helmholtz instability structures to the EW direction and the curved stripped tail is extended to the SE. There are also cavities in the core. See Machacek et al. (2006a) for the discussions on the gas stripping, Machacek et al. (2006b) on the nuclear outflow and Roedigger et al. (2015) on theoretical modeling in terms of viscosity and KH instability. The T maps clearly show the extended tail filled with ~0.6 keV gas. The T profile shows a hot core, having a negative T gradient in the central region, a minimum (T ~ 0.4 keV) at 4-5 kpc, and then a positive gradient in the outer region.

 

NGC 4555 (d=91.5 Mpc,  1 = 26.6 kpc,  re=13.2 kpc,  r25=25.4 kpc)

It is an isolated elliptical, but its relatively high gas temperature (TGAS ~ 1 keV) and luminosity (LX ~1041.5 erg s-1) may indicate a dominant galaxy in a very poor group with a massive dark halo (O'Sullivan & Ponman 2004). The 2D maps indicate that the hot gas is smooth and relaxed. The T map and profile suggest the presence of a cool core.

 

NGC 4594 (d=9.8 Mpc,  1 = 2.8 kpc,  re=3.4 kpc,  r25=12.4 kpc)

It is a nearby edge-on S0 galaxy, also known as M104 and Sombrero. Its nucleus and X-ray binaries dominate the entire X-ray emission (Li et al. 2011). After excluding point sources, the temperature map suggests that low temperature (~0.5 keV) gas lies along the disk to the EW of the core. The gas to the perpendicular direction from the disk is slightly hotter (~0.7 keV).

 

NGC 4636 (d=14.7 Mpc,  1 = 4.3 kpc,  re=6.7 kpc,  r25=12.8 kpc)

It is one of extensively studied hot gas rich elliptical galaxy in the Virgo cluster, at 10° to the S from the Virgo cluster center and at the northern end of the Virgo South Extension (centered around NGC 4697). The hot gas exhibits spiral-arm like features and cavities on a small scale (< 10 kpc), extension to the WSW on an intermediate scale (10-30 kpc) and another extension to the N on a large scale (> 50 kpc). The smaller scale features are related to the nuclear activities and radio jets and the larger scale features are likely sloshing due to the perturbation from nearby galaxies (O’Sullivan et al. 2005, Baldi et al. 2009). As seen in the SB maps, both T profile and map indicate complex thermal structures. The temperature of the hot gas is about 0.5 keV in the central region, increases to ~1 keV at ~15 kpc, then declines in the outer region. The T maps further show the asymmetric distribution of the inner cooler gas which is elongated to the N-S direction.

 

NGC 4649 (d=16.8 Mpc,  1 = 4.9 kpc,  re=6.2 kpc,  r25=18.1 kpc)

It is a giant elliptical galaxy in the Virgo cluster, at 3.3° to the E from the cluster center, also known as M60. It hosts a large amount of hot gas which had been considered as a prototype example of a smooth, relaxed hot halo. However, Chandra observations revealed the non-smooth, asymmetric features both on a small (< 3 kpc) scale related to the AGN activity (Paggi et al. 2014) and a large scale (20-30 kpc) related to the bulk motion (Wood et al. 2017). Also detected in the same fov is a nearby spiral galaxy, NGC 4647, located at 2.5′ form NGC 4649 in the NW direction.  The temperature profile shows a negative gradient inside and a positive gradient outside with a minimum (T ~ 0.8 keV) at r ~ 1 kpc. A hot core in the center has been discussed in Pellegrini et al. (2012) and Paggi et al. (2014). The temperature map further indicates that the cooler gas (0.8-0.9 keV) extends preferentially to the NE and SW directions, the same directions where two extended wings are visible while the gas in the other directions (NW and SE) is hotter (1-1.2 keV). Woods et al. (2017) suggested that the two wings might be caused by the Kelvin-Helmholtz instability while the galaxy is infalling toward the center of the Virgo cluster. However, the cooler gas extended from the center may imply that the extended wings may also be related to the AGN outflows.

 

NGC 4782 (d=60.0 Mpc,  1 = 17.5 kpc,  re=4.4 kpc,  r25=15.5 kpc)

It is in a close pair VV201 with NGC 4783, aka Dumbbell galaxies. NGC 4782 is also a FR-I radio galaxy (3C278). The hot ISM (~0.5 keV) in both galaxies is embedded inside the hotter (~1.4 keV) ICM (see Machacek et al. 2007). The hot gas is highly disturbed. The hot gas in NGC 4782 exhibits a cavity and X-ray knots which are related to the radio jets and the hot gas of NGC 4783 exhibits a head-tail structure (a cold front and an extended tail) caused by the ram pressure as it is apparently moving to the E.

 

NGC 5044 (d=31.2 Mpc,  1 = 9.1 kpc,  re=3.9 kpc,  r25=13.4 kpc)

It is a dominant galaxy in the X-ray brightest group in the sky. Its extended hot halo has been extensively studied from the early X-ray missions. The deep Chandra observations show the hot gas is sloshing with fronts visible in surface brightness and abundance, temperature maps with many small cavities (David et al. 2009, 2011, 2017). Also shown in XMM-Newton data is a large scale sloshing (O'Sullivan et al (2014)

 

NGC 5129 (d=103.0 Mpc,  1 = 30.0 kpc,  re=14.3 kpc,  r25=25.4 kpc)

It is the dominant galaxy in a small group (Eckmiller et al. 2011, see also Bharadwaj et al. 2014).

The hot gas has a cool core with a positive temperature gradient in the inner region to a peak (~1 keV) at r ~ 20 kpc and a negative gradient in the outer region to the fov limit (rmax~ 200 kpc).

 

NGC 5171 (d=100.0 Mpc, 1 = 29.1 kpc,  re=12.4 kpc,  r25=15.9 kpc)

It is the dominant galaxy in a small group with multiple roughly-equal sized ellipticals. The hot ISM (LX ~ a few x 1040 erg s-1) directly associated with NGC 5171 is confined within r­e with T ~ 1 keV and is roughly symmetric inside re. Interestingly, there is a large amount ((LX ~ a few x 1041 erg s-1) of hotter gas (1.2-1.3 keV) filling gaps among group galaxies (see also Osmond et al. 2004), mostly to the N and the E from NGC 5171. Also detected in a single Chandra observation are three large galaxies (NGC 5179, NGC 5176 and NGC 5177) and two small galaxies (SDSS J132920.65+114424.1 and SDSS J132928.18+114625.2). The temperatures of their hot ISM are in the range of 0.3-0.6 keV (see also Jeltema et al. 2008).

 

---------------------------------------------------------

 name       RA          DEC         D(′)      PA(deg)   

          (J2000)      (J2000)   from N5171  from N5171 

---------------------------------------------------------

 N5176    202.35399   11.78148       2.9′       17

 N5177    202.35108   11.79703       3.8′       10

 N5179    202.37869   11.74583       2.4′       74

 

 SDSS J132920.65+114424.1            0.4′      326

 SDSS J132928.18+114625.2            2.8′       35

---------------------------------------------------------

 

NGC 5813 (d=32.2 Mpc,  1 = 9.4 kpc,  re=8.3 kpc,  r25=19.5 kpc)

It is the dominant galaxy in a small group. The hot gas morphology exhibits three sets of nested co-aligned cavities and shocks (Randall et al. 2011 and 2015). The temperature map shows cooler uplifted material along line of cavities.

 

NGC 5846 (d=24.9 Mpc,  1 = 7.2 kpc,  re=7.2 kpc,  r25=14.7 kpc)

It is the dominant galaxy in a small group. The hot gas morphology exhibits small-scale cavities associated with radio jets in the central region and spiral-like tails and multiple cold fonts on a large scale which may be caused by sloshing due to a nearby galaxy NGC 5850 (Machacek et al. 2011, Gastadello et al. 2013, Paggi et al. 2017).

 

N5866 (d=15.4 Mpc,  1 = 4.5 kpc,  re=2.8 kpc,  r25=10.4 kpc)

It is a nearby edge-on S0 galaxy, hosting a LINER nucleus. It could be M102 that has not been identified unambiguously. Li et al (2009) investigated the weak diffuse hot gas which is extended as far as 3.5 kpc away from the galactic plane. The faint spiral-like filament to the S lying outside the D25 ellipse may be interesting, but needs to be confirmed by deeper observations.

 

NGC 6107 (d=127.9 Mpc,  1 = 37.2 kpc,  re=16.3 kpc,  r25=15.8 kpc)

It is the dominant galaxy in a small group. The hot ISM (~1 keV) inside the D25 ellipse shows an elongated structure in the SE-NW direction (roughly along the minor axis), which is surrounded by the hotter (~1.5 keV) gas. The large scale ROSAT observation (Feretti et al 1995) showed that the hotter IGM extends to the entire regions connecting NGC 6107 and NGC 6109 (at 7.5 to the NE from NGC 6107). It is also known as a radio galaxy, B2 1615+35, with a SE-NW radio extension (Feretti et al 1995, Condon et al. 2002), which is interestingly along the same direction with the inner hot gas feature.

 

NGC 6338 (d=123.0 Mpc,  1 = 35.8 kpc,  re=17.1 kpc,  r25=27.1 kpc)

It is the dominant galaxy in a small group, possibly merging with PGC 59943 (or MCG +10-24-117) at 1.2 arcmin to the N. Both galaxies have stripped tails and multiple cavities (Pandge et el. 2012). The tail of PGC 59943 is stretched to the N, indicating that this galaxy is moving to the S. In this ACIS-I image, the chip gaps are visible in raw binned images and some spectral maps, mostly significant in CB (because a spatial bin was determined in a region with similar counts/area) but least in WB. The T profile and map show the presence of a cool core inside re.

 

NGC 6482 (d=58.4 Mpc,  1 = 17.0 kpc,  re=6.3 kpc,  r25=16.9 kpc)

It is an isolated elliptical or a fossil group galaxy with a relatively relaxed hot gas morphology (Khoroshahi et al 2004; Buote 2017). In contrast to typical relaxed systems, the hot gas is hotter in the inner region than in the outer region with the temperature monotonically decreasing outward from 0.9 keV at the center to 0.5 keV at 50 kpc. The Suzaku data suggest a hint that the temperature may increase slightly (to 0.65 keV) at the outer region ~100 kpc (Buote 2017). All spectral maps show roughly circularly symmetric distribution, except in the inner 10 kpc region where the hotter gas is slightly elongated to the SE-NW direction (roughly along the minor axis direction), more pronounced to the SE.

 

NGC 6861 (d=28.0 Mpc,  1 = 8.2 kpc,  re=3.1 kpc,  r25=11.5 kpc)

It is one of the two dominant galaxies (with NGC 6868 at 26 to the E) in the Telescopium galaxy group. While NGC 6861 is slightly less luminous (by a factor of 1.4) than NGC 6868, but its velocity dispersion is higher (by a factor or 1.7). The hot gas morphology indicates the two galaxies (or two subgroups) are possibly merging. The hot gas in NGC 6861 has bifurcated tails trailing NGC 6861 at ~40 kpc to the W and NW, likely caused by the subgroup merger (Machacek et al. 2010).

 

NGC 6868 (d=26.8 Mpc,  1 = 7.8 kpc,  re=3.9 kpc,  r25=13.8 kpc)

It is one of the two dominant galaxies in the Telescopium galaxy group, possibly merging with NGC 6861 at 26 to the W. There is a cold font at ~23 kpc to the N, likely caused by sloshing due to the merger (Machacek et al. 2010). The T maps further show an asymmetry in the hot gas morphology with slightly cold gas (~0.6 keV) forming a shell-like feature which is more pronounced to the NE than to the S on a scale of the D25 ellipse.

 

NGC 7618 (d=74.0 Mpc,  1 = 21.5 kpc,  re=7.7 kpc,  r25=12.9 kpc)

It is a dominant galaxy in a small group, showing an excellent example of the pronounced spiral-like features caused by sloshing and the associated structures caused by turbulent instability. It is likely merging with UGC 12491 (PGC 71014), at 14 to the NW from NGC 7618 (Kraft et al. 2006, Roediger et al. 2012). The T maps clearly show the curved, extended tail filled with 0.7-0.8 keV gas which is surrounded by ~1.2 keV hotter ambient gas. Note that the tail is more pronounced in the T map than in the SB map. The tail is clearly visible in the EM and projected entropy maps, but almost invisible in the projected pressure map, possibly indicating pressure balance with the ambient gas.

 

N7619 (d=53.0 Mpc,  1= 15.4 kpc,  re=8.8 kpc,  r25=19.4 kpc)

It is a dominant E galaxy in the Pegasus I group. It has a cold front to the NE and extended tails to the SW. The X-ray tail is metal-enriched suggesting that the hot gas is originated from the galaxy (Kim et al. 2008). A nearby galaxy, NGC 7626, at 7to the E is possibly interacting with NGC 7619.

 

NGC 7626 (d=56.0 Mpc,  1 = 16.3 kpc,  re=12.0 kpc,  r25=21.4 kpc)

It is an E galaxy in the Pegasus I group at 7 to the E from the NGC 7619. The surface brightness and temperature maps suggest that it is possibly merging with NGC 7619 (Randall et al. 2009).

 


 

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