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Register a new userProbing Evolutionary Mechanisms in Galaxy Clusters: Neutral Atomic Hydrogen in Abell 1367
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We present VLA H I imaging data for a field in the NW of the galaxy cluster Abell 1367 (z = 0.02) in an attempt to probe the effect environment has on the interstellar medium of late-type spiral galaxies. Several galaxies show pronounced tails and asymmetries, and 7 out of 10 show significant, several kpc offsets between the HI centroid and the optical. We compare our results against a sample of optically bright, late-type galaxies (spirals) across the central 1.5 Mpc of the cluster taken from the Arecibo Galaxy Environment Survey (AGES). We calculate the H I deficiency and find that the expected global trend for the H I deficiency of these spirals to increase with projected proximity to the cluster core, seen in clusters like Coma and Virgo, is not observed. We classified the spirals into four evolutionary states, with the galaxies in each state sharing a similar degree of H I deficiency and optical colour. The common characteristics of the spirals in each evolutionary state suggests they have been subject to similar environmental processes. Many of the spirals in the most common evolutionary state (moderate H I deficiency and blue colour) have an H I intensity maximum which is displaced relative to its optical counterpart. The orientation of these offsets and magnitude of their H I deficiencies together with data from other wavelengths provide observational evidence in support of varying degrees of ram pressure stripping and tidal interaction. In general, our results indicate that the H I disks of bright late-type galaxies in the central part of the cluster are subject to both gas loss and morphological disturbance as a result of their interaction with the cluster environment. This provides further observational evidence of a more complex environment in Abell 1367 as compared to Virgo and Coma.
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Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red sequence lenticular galaxies and blue cloud galaxies, low mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally-driven gas flows toward the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red sequence or blue cloud galaxies, at fixed stellar mass, with location within the cluster.
By means of zoom-in hydrodynamic simulations we quantify the amount of neutral hydrogen (HI) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics (SPH), include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split in two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analyzed to account for HI self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter halos monotonically increases with the halo mass and can be well described by a power-law of the form $M_{rm HI}(M,z)propto M^{3/4}$. Our results point out that AGN feedback reduces both the total halo mass and its HI mass, although it is more efficient in removing HI. We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by $sim50%$, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within halos is also affected by AGN feedback, whose effect is to decrease the fraction of HI that resides in the halo inner regions. By extrapolating our results to halos not resolved in our simulations we derive astrophysical implications from the measurements of $Omega_{rm HI}(z)$: halos with circular velocities larger than $sim25~{rm km/s}$ are needed to host HI in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of $Omega_{rm HI}b_{rm HI}$ derived from available 21cm intensity mapping observations.
Multi-wavelength observations show that Abell 1367 (A1367) is a dynamically young cluster, with at least two subclusters merging along the SE-NW direction. With the wide-field XMM-Newton mosaic of A1367, we discover a previously unknown merger shock at the NW edge of the cluster. We estimate the shock Mach number from the density and temperature jumps as $M_{rho}=1.21pm0.08$ and $M_T=1.60pm0.07$, respectively. This shock region also corresponds to a radio relic discovered with the VLA and GBT, which could be produced by the shock re-acceleration of pre-existing seed relativistic electrons. We suggest that some of the seed relativistic electrons originate from late-type, star-forming galaxies in this region.
We present VLA D-array HI observations of the RSCG42 and FGC1287 galaxy groups, in the outskirts of the Abell 1367 cluster. These groups are projected ~ 1.8 and 2.7 Mpc west from the cluster centre. The Arecibo Galaxy Environment survey provided evidence for HI extending over as much as 200kpc in both groups. Our new, higher resolution observations reveal that the complex HI features detected by Arecibo are in reality two extraordinary long HI tails extending for ~160 and 250 kpc, respectively, i.e., among the longest HI structures ever observed in groups of galaxies. Although in the case of RSCG42 the morphology and dynamics of the HI tail, as well as the optical properties of the group members, support a low-velocity tidal interaction scenario, less clear is the origin of the unique features associated with FGC1287. This galaxy displays an exceptionally long dog leg HI tail and the large distance from the X-ray emitting region of Abell 1367 makes a ram-pressure stripping scenario highly unlikely. At the same time a low-velocity tidal interaction seems unable to explain the extraordinary length of the tail and the lack of any sign of disturbance in the optical properties of FGC1287. An intriguing possibility could be that this galaxy might have recently experienced a high-speed interaction with another member of the Coma-Abell 1367 Great Wall. We searched for the interloper responsible for this feature and, although we find a possible candidate, we show that without additional observations it is impossible to settle this issue. While the mechanism responsible for this extraordinary HI tail remains to be determined, our discovery highlights how little we know about environmental effects in galaxy groups.
We present CO (J = 1 - 0) and CO (J = 2 - 1) spectra for 19 bright, late-type galaxies (spirals) in the central region of the galaxy cluster Abell 1367 (z = 0.02) from observations made with the IRAM 30 - m telescope. All 19 spirals were observed at the position of their optical center and for a subset, at multiple positions. For each spiral the integrated CO (J = 1 - 0) intensity from the central pointing, in few cases supplemented with intensities from offset pointings, was used to estimate its molecular hydrogen mass and H_2 deficiency. Accepting the considerable uncertainties involved in determining H_2 deficiencies, spirals previously identified by us to have redder colours and higher HI deficiencies as a result of environmental influence, were found to be more H_2 deficient compared to members of the sample in less advanced evolutionary states. For eight of the observed spirals multiple pointing observations were made to investigate the distribution of their molecular gas. For these spirals we fitted Gaussians to the CO intensities projected in a line across the galaxy. In two cases, CGCG 097-079 and CGCG 097-102(N), the offset between the CO and optical intensity maxima was significantly larger than the pointing uncertainty and the FWHMs of the fits were significantly greater than those of the other spirals, irrespective of optical size. Both signatures are indicators of an abnormal molecular gas distribution. In the case of CGCG 097-079, which is considered an archetype for ram pressure stripping, our observations indicate the CO intensity maximum lies ~ 15.6 +/- 8.5 arcsec (6 kpc) NW of the optical centre at the same projected position as the HI intensity maximum.
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