Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEnvironments of QSOs at intermediate redshifts
76
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A preliminary analysis of fields around 20 mainly radio-quiet QSOs (RQQs) at intermediate redshift is summarized. We find overdensities of faint sources around 50% of our observed QSOs suggesting that they are located in groups or even clusters of galaxies.
rate research
Read More
We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z>6 from a range of surveys: the SDSS, the CFHT-LS, FIRST, Spitzer and UKIDSS. The WISE catalog thus provides a substantial increase in the quantity of IR data available for these sources: 17 are detected in the WISE W1 (3.4-micron) band, 16 in W2 (4.6-micron), 3 in W3 (12-micron) and 0 in W4 (22-micron). This is particularly important with Spitzer in its warm-mission phase and no faint follow-up capability at wavelengths longwards of 5 microns until the launch of JWST. WISE thus provides a useful tool for understanding QSOs found in forthcoming large-area optical/IR sky surveys, using PanSTARRS, SkyMapper, VISTA, DES and LSST. The rest-UV properties of the WISE-detected and the WISE-non-detected samples differ: the detections have brighter i/z-band magnitudes and redder rest-UV colors. This suggests that a more aggressive hunt for very-high-redshift QSOs, by combining WISE W1 and W2 data with red observed optical colors could be effective at least for a subset of dusty candidate QSOs. Stacking the WISE images of the WISE-non-detected QSOs indicates that they are on average significantly fainter than the WISE-detected examples, and are thus not narrowly missing detection in the WISE catalog. The WISE-catalog detection of three of our sample in the W3 band indicates that their mid-IR flux can be detected individually, although there is no stacked W3 detection of sources detected in W1 but not W3. Stacking analyses of WISE data for large AGN samples will be a useful tool, and high-redshift QSOs of all types will be easy targets for JWST.
The nature of absorption-selected galaxies and their connection to the general galaxy population have been open issues for more than three decades, with little information available on their gas properties. Here we show, using detections of carbon monoxide (CO) emission with the Atacama Large Millimeter/submillimeter Array (ALMA), that five of seven high-metallicity, absorption-selected galaxies at intermediate redshifts, $z approx 0.5-0.8$, have large molecular gas masses, $M_{rm Mol} approx (0.6 - 8.2) times 10^{10} : {rm M}_odot$ and high molecular gas fractions ($f_{rm Mol} equiv : M_{rm Mol}/(M_ast + M_{rm Mol}) approx 0.29-0.87)$. Their modest star formation rates (SFRs), $approx (0.3-9.5) : {rm M}_odot$ yr$^{-1}$, then imply long gas depletion timescales, $approx (3 - 120)$ Gyr. The high-metallicity absorption-selected galaxies at $z approx 0.5-0.8$ appear distinct from populations of star-forming galaxies at both $z approx 1.3-2.5$, during the peak of star formation activity in the Universe, and lower redshifts, $z lesssim 0.05$. Their relatively low SFRs, despite the large molecular gas reservoirs, may indicate a transition in the nature of star formation at intermediate redshifts, $z approx 0.7$.
We present a sample of $i_{775}$-dropout candidates identified in five Hubble Advanced Camera for Surveys fields centered on Sloan Digital Sky Survey QSOs at redshift $zsim 6$. Our fields are as deep as the Great Observatory Origins Deep Survey (GOODS) ACS images which are used as a reference field sample. We find them to be overdense in two fields, underdense in two fields, and as dense as the average density of GOODS in one field. The two excess fields show significantly different color distributions from that of GOODS at the 99% confidence level, strengthening the idea that the excess objects are indeed associated with the QSO. The distribution of $i_{775}$-dropout counts in the five fields is broader than that derived from GOODS at the 80% to 96% confidence level, depending on which selection criteria were adopted to identify $i_{775}$-dropouts; its width cannot be explained by cosmic variance alone. Thus, QSOs seem to affect their environments in complex ways. We suggest the picture where the highest redshift QSOs are located in very massive overdensities and are therefore surrounded by an overdensity of lower mass halos. Radiative feedback by the QSO can in some cases prevent halos from becoming galaxies, thereby generating in extreme cases an underdensity of galaxies. The presence of both enhancement and suppression is compatible with the expected differences between lines of sight at the end of reionization as the presence of residual diffuse neutral hydrogen would provide young galaxies with shielding from the radiative effects of the QSO.
We present 350micron observations of 36 ultraluminous infrared galaxies (ULIRGs) at intermediate redshifts (0.089 <= z <= 0.926) using the Submillimeter High Angular Resolution Camera II (SHARC-II) on the Caltech Submillimeter Observatory (CSO). In total, 28 sources are detected at S/N >= 3, providing the first flux measurements longward of 100micron for a statistically significant sample of ULIRGs in the redshift range of 0.1 < z < 1.0. Combining our 350micron flux measurements with the existing IRAS 60 and 100micron data, we fit a single-temperature model to the spectral energy distribution (SED), and thereby estimate dust temperatures and far-IR luminosities. Assuming an emissivity index of beta = 1.5, we find a median dust temperature and far-IR luminosity of Td = 42.8+-7.1K and log(Lfir/Lsolar) = 12.2+-0.5, respectively. The far-IR/radio correlation observed in local star-forming galaxies is found to hold for ULIRGs in the redshift range 0.1 < z < 0.5, suggesting that the dust in these sources is predominantly heated by starbursts. We compare the far-IR luminosities and dust temperatures derived for dusty galaxy samples at low and high redshifts with our sample of ULIRGs at intermediate redshift. A general Lfir-Td relation is observed, albeit with significant scatter, due to differing selection effects and variations in dust mass and grain properties. The relatively high dust temperatures observed for our sample compared to that of high-z submillimeter-selected starbursts with similar far-IR luminosities suggest that the dominant star formation in ULIRGs at moderate redshifts takes place on smaller spatial scales than at higher redshifts.
We present the first study of large-scale bars in clusters at intermediate redshifts (z=0.4-0.8). We compare the properties of the bars and their host galaxies in the clusters with those of a field sample in the same redshift range. We use a sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. The morphological classification of the galaxies and the detection of bars are based on deep HST/ACS F814W images. The total optical bar fraction in the redshift range z=0.4-0.8, averaged over the entire sample, is 25%. This is lower than found locally, but in good agreement with studies of bars in field environments at intermediate redshifts. For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. In agreement with local studies, we find that disk-dominated galaxies have a higher bar fraction than bulge-dominated galaxies. We also find, based on a small subsample, that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher than at larger distances.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
