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Register a new userAn XMM-Newton study of the RGH 80 galaxy group
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We present an X-ray study of the galaxy group RGH 80, observed by XMM-Newton. The X-ray emission of the gas is detected out to ~ 462h^{-1}_{50} kpc, corresponding to ~ 0.45 r_{200}. The group is relatively gas rich and luminous with respect to its temperature of 1.01 +/- 0.01 keV. Using the deprojected spectral analysis, we find that the temperature peaks at ~ 1.3 keV around 0.11r_{200}, and then decreases inwards to 0.83 keV at the center and outwards to ~ 70% of the peak value at large radii. Within the central ~ 60 kpc of the group where the gas cooling time is less than the Hubble time, two-temperature model with temperatures of 0.82 and 1.51 keV and the Galactic absorption gives the best fit of the spectra, with ~ 20% volume occupied by the cool component. We also derive the gas entropy distribution, which is consistent with the prediction of cooling and/or internal heating models. Furthermore, the abundances of O, Mg, Si, S, and Fe decrease monotonically with radius. With the observed abundance ratio pattern, we estimate that ~ 85% or ~ 72% of the iron mass is contributed by SN Ia, depending on the adopted SN II models.
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By creating and analyzing the two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with the high-quality Chandra data, we detect a high-abundance ($simeq 0.7$ $Z_odot$) arc, where the metal abundance is significantly higher than the surrounding regions by $simeq 0.3$ Z_odot$. This structure shows tight spatial correlations with the member galaxy PGC 046529, as well as with the arm-like feature identified on the X-ray image in the previous work of Randall et al. (2009). Since no apparent signature of AGN activity is found associated with PGC 046529 in multi-band observations, and the gas temperature, metallicity, and mass of the high-abundance arc resemble those of the ISM of typical early-type galaxies, we conclude that this high-abundance structure is the remnant of the ISM of PGC 046529, which was stripped out of the galaxy by ram pressure stripping due to the motion of PGC 046529 in RGH 80. This novel case shows that ram pressure stripping can work efficiently in the metal enrichment process in galaxy groups, as it can in galaxy clusters.
While theory and simulations indicate that galaxy mergers play an important role in the cosmological evolution of accreting black holes and their host galaxies, samples of Active Galactic Nuclei (AGN) in galaxies at close separations are still small. In order to increase the sample of AGN pairs, we undertook an archival project to investigate the X-ray properties of a SDSS-selected sample of 32 galaxy pairs with separations $le$150 kpc containing one optically-identified AGN, that were serendipitously observed by XMM-Newton. We discovered only one X-ray counterpart among the optically classified non-active galaxies, with a weak X-ray luminosity ($simeq$5$times$10$^{41}$ erg s$^{-1}$). 59% (19 out of 32) of the AGN in our galaxy pair sample exhibit an X-ray counterpart, covering a wide range in absorption corrected X-ray luminosity (5$times$10$^{41}$-2$times$10$^{44}$ erg s$^{-1}$). More than 79% of these AGN are obscured (column density $N_H>$10$^{22}$ cm$^{-2}$), with more than half thereof ({it i.e.}, about 47% of the total AGN sample) being Compton-thick. AGN/no-AGN pairs are therefore more frequently X-ray obscured (by a factor $simeq$1.5) than isolated AGN. When compared to a luminosity and redshift-matched sample of {it bona fide} dual AGN, AGN/no-AGN pairs exhibit one order-of-magnitude lower X-ray column density in the same separation range ($>$10 kpc). A small sample (4 objects) of AGN/no-AGN pairs with sub-pc separation are all heavily obscured, driving a formal anti-correlation between the X-ray column density and the galaxy pair separation in these systems. These findings suggest that the galactic environment has a key influence on the triggering of nuclear activity in merging galaxies.
In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. We correlate these newly detected sources with earlier M 33 X-ray catalogues and information from optical, infra-red and radio wavelengths. As M 33 sources we detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources, and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations we would expect 175 to 210 background sources in this field. This indicates that about half of the sources detected are sources within M 33.
This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentration of starburst or AGN activity in the nearby Universe. So it is a veritable laboratory for the study of the relationship between galaxy interactions and nuclear activity. Previous optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was unclear. Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocally reveals a heavily obscured AGN and a separately identified thermal (starburst) plasma, in NGC 835, NGC 833 and NGC 839. NGC 838 shows only starburst thermal emission. Starbursts and AGN can evidently coexist in members of this highly evolved system of merged and merging galaxies, implying a high probability for the formation of AGN as well as starbursts in post-merger galaxies.
The distribution of hot interstellar medium in early-type galaxies bears the imprint of the various astrophysical processes it underwent during its evolution. The X-ray observations of these galaxies have identified various structural features related to AGN and stellar feedback and environmental effects such as merging and sloshing. In our XMM-Newton Galaxy Atlas (NGA) project, we analyze archival observations of 38 ETGs, utilizing the high sensitivity and large field of view of XMM-Newton to construct spatially resolved 2D spectral maps of the hot gas halos. To illustrate our NGA data products in conjunction with the Chandra Galaxy Atlas (Kim et al. 2019), we describe two distinct galaxies - NGC 4636 and NGC 1550, in detail. We discuss their evolutionary history with a particular focus on the asymmetric distribution of metal-enriched, low-entropy gas caused by sloshing and AGN- driven uplift. We will release the NGA data products to a dedicated website, which users can download to perform further analyses.
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