Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMulti-wavelength study of X-ray luminous clusters at z ~ 0.3 I. Star formation activity of cluster galaxies
95
0
0.0
(
0
)
Authors
F. G. Braglia
Ask ChatGPT about the research
No Arabic abstract
The current paradigm of cosmic formation and evolution of galaxy clusters foresees growth mostly through merging. Galaxies in the infall region or in the core of a cluster undergo transformations owing to different environmental stresses. For two X-ray luminous clusters at redshift z ~ 0.3 with opposite X-ray morphologies, RXCJ0014.3-3022 and RXCJ2308.3-0211, we assess differences in galaxy populations as a function of cluster topography. Cluster large-scale structure and substructure are determined from the combined photometry in the B, V, and R bands, and from multi-object optical spectroscopy at low resolution. A spectral index analysis is performed, based on the [OII] and Hdelta features, and the D4000 break, available for more than 100 member galaxies per cluster. Combination of spectral indices and FUV-optical colours provides a picture of the star formation history in galaxies. In spite of the potential presence of a small fraction of galaxies with obscured star formation activity, the average star-formation history of cluster members is found to depend on cluster-centric distance and on substructure. There is a sharp increase in star formation activity along two well-defined filamentary structures of the merging cluster RXCJ0014.3-3022, out to its virial radius and beyond, produced by luminous (L ~ L*) and sub-L* galaxies. Conversely, the regular cool-core cluster RXCJ2308.3-0211 mostly hosts galaxies which either populate the red sequence or are becoming passive. These results suggest the existence of a correspondence between assembly state and overall age of the stellar populations of galaxies inside the virialized region and in the surrounding large scale structure of massive clusters at z ~ 0.3. (Abridged)
rate research
Read More
We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M$_{ast}$ $sim$ 10$^{10}$ M$_odot$) IRAC- and MIPS 24$mu$m-detected Lyman Break Galaxies (LBGs) with spectroscopic redshifts z$sim$3 in the GOODS-North field (L$_{rm UV}$$>1.8times$L$^{ast}_{z=3}$). For LBGs without individual 24$mu$m detections, we employ stacking techniques at 24$mu$m, 1.1mm and 1.4GHz, to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a Luminous Infrared Galaxy (LIRG) with L$rm_{IR}$=4.5$^{+1.1}_{-2.3}$$times 10^{11}$ L$_{odot}$ and a specific star formation rate (SSFR) of 4.3 Gyr$^{-1}$ that corresponds to a mass doubling time $sim$230 Myrs. On the other hand, when considering the 24$mu$m-detected LBGs we find among them galaxies with L$rm_{IR}> 10^{12}$ L$_{odot}$, indicating that the space density of $zsim$3 UV-selected Ultra-luminous Infrared Galaxies (ULIRGs) is $sim$(1.5$pm$0.5)$times 10^{-5}$ Mpc$^{-3}$. We compare measurements of star formation rates (SFRs) from data at different wavelengths and find that there is tight correlation (Kendalls $tau >$ 99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, mm and radio data for the whole range of L$rm_{IR}$ up to L$rm_{IR}$ $sim$ 10$^{13}$ L$_{odot}$. This range is greater than that for which the correlation is known to hold at z$sim$2, possibly due to the lack of significant contribution from PAHs to the 24$mu$m flux at $zsim$3. The fact that this agreement is observed for galaxies with L$rm_{IR}$ $>$ 10$^{12}$ L$_{odot}$ suggests that star-formation in UV-selected ULIRGs, as well as the bulk of star-formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at $z=2$.
Observational galaxy cluster studies at z>1.5 probe the formation of the first massive M>10^14 Msun dark matter halos, the early thermal history of the hot ICM, and the emergence of the red-sequence population of quenched early-type galaxies. We present first results for the newly discovered X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.555, detected and confirmed by the XMM-Newton Distant Cluster Project (XDCP) survey. We selected the system as a serendipitous weak extended X-ray source in XMM-Newton archival data and followed it up with two-band near-infrared imaging and deep optical spectroscopy. We can establish XMMU J1007.4+1237 as a spectroscopically confirmed, massive, bona fide galaxy cluster with a bolometric X-ray luminosity of Lx=(2.1+-0.4)times 10^44 erg/s, a red galaxy population centered on the X-ray emission, and a central radio-loud brightest cluster galaxy. However, we see evidence for the first time that the massive end of the galaxy population and the cluster red-sequence are not yet fully in place. In particular, we find ongoing starburst activity for the third ranked galaxy close to the center and another slightly fainter object. At a lookback time of 9.4Gyr, the cluster galaxy population appears to be caught in an important evolutionary phase, prior to full star-formation quenching and mass assembly in the core region. X-ray selection techniques are an efficient means of identifying and probing the most distant clusters without any prior assumptions about their galaxy content.
We present a study of X-ray AGN overdensities in 16 Abell clusters, within the redshift range 0.073<z<0.279, in order to investigate the effect of the hot inter-cluster environment on the triggering of the AGN phenomenon. The X-ray AGN overdensities, with respect to the field expectations, were estimated for sources with L_x>= 10^{42} erg s^{-1} (at the redshift of the clusters) and within an area of 1 h^{-1}_{72} Mpc radius (excluding the core). To investigate the presence or not of a true enhancement of luminous X-ray AGN in the cluster area, we also derived the corresponding optical galaxy overdensities, using a suitable range of $r$-band magnitudes. We always find the latter to be significantly higher (and only in two cases roughly equal) with respect to the corresponding X-ray overdensities. Over the whole cluster sample, the mean X-ray point-source overdensity is a factor of ~4 less than that corresponding to bright optical galaxies, a difference which is significant at a >0.995 level, as indicated by an appropriate t-student test. We conclude that the triggering of luminous X-ray AGN in rich clusters is strongly suppressed. Furthermore, searching for optical SDSS counterparts of all the X-ray sources, associated with our clusters, we found that about half appear to be background QSOs, while others are background and foreground AGN or stars. The true overdensity of X-ray point sources, associated to the clusters, is therefore even smaller than what our statistical approach revealed.
We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5sigma) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f(r<40)=(1.5+-0.3)x10^(-14) erg/s/cm2. Optical/NIR follow-up observations confirmed the presence of an overdensity of red galaxies matching the X-ray emission. The cluster was spectroscopically confirmed to be at z=1.579 using ground-based VLT/FORS2 spectroscopy. The analysis of the I-H colour-magnitude diagram shows a sequence of red galaxies with a colour range [3.7 < I-H < 4.6] within 1 from the cluster X-ray emission peak. However, the three spectroscopic members (all with complex morphology) have significantly bluer colours relative to the observed red-sequence. In addition, two of the three cluster members have [OII] emission, indicative of on-going star formation. Using the spectroscopic redshift we estimated the X-ray bolometric luminosity, Lbol = 5.8x10^44 erg/s, implying a massive galaxy cluster. This places XMMU J0044.0-2033 at the forefront of massive distant clusters, closing the gap between lower redshift systems and recently discovered proto- and low-mass clusters at z >1.6.
Nuclear starbursts and AGN activity are the main heating processes in luminous infrared galaxies (LIRGs) and their relationship is fundamental to understand galaxy evolution. In this paper, we study the star-formation and AGN activity of a sample of 11 local LIRGs imaged with subarcsecond angular resolution at radio (8.4GHz) and near-infrared ($2.2mu$m) wavelengths. This allows us to characterize the central kpc of these galaxies with a spatial resolution of $simeq100$pc. In general, we find a good spatial correlation between the radio and the near-IR emission, although radio emission tends to be more concentrated in the nuclear regions. Additionally, we use an MCMC code to model their multi-wavelength spectral energy distribution (SED) using template libraries of starburst, AGN and spheroidal/cirrus models, determining the luminosity contribution of each component, and finding that all sources in our sample are starburst-dominated, except for NGC6926 with an AGN contribution of $simeq64$%. Our sources show high star formation rates ($40$ to $167M_odotmathrm{yr}^{-1}$), supernova rates (0.4 to $2.0mathrm{SN}mathrm{yr}^{-1}$), and similar starburst ages (13 to $29mathrm{Myr}$), except for the young starburst (9Myr) in NGC6926. A comparison of our derived star-forming parameters with estimates obtained from different IR and radio tracers shows an overall consistency among the different star formation tracers. AGN tracers based on mid-IR, high-ionization line ratios also show an overall agreement with our SED model fit estimates for the AGN. Finally, we use our wide-band VLA observations to determine pixel-by-pixel radio spectral indices for all galaxies in our sample, finding a typical median value ($alphasimeq-0.8$) for synchrotron-powered LIRGs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
