An Optical/Near‐Infrared Study of Radio‐loud Quasar Environments. II. Imaging Results

I present the data for an optical/near-infrared study of radioloud quasar (RLQ) environments from to and z 5 0.6 z 5 2.0 the analysis of the data from to . I thoroughly z 5 1.0 z 5 2.0 discuss the sample selection, observing, data reduction, and object cataloging techniques. I find a significant excess of galaxies in the fields K * 19 of 31 RLQs, on two spatial scales. One component is z 5 1–2 at from the quasars and is significant compared to the ′′ v ! 40 galaxy surface density at in the same fields. The other ′′ v 1 40 component appears roughly constant across the fields to v ∼ from the quasars and is significant compared to the galaxy ′′ 100 surface density seen in random-field surveys in the literature. The component may be produced by as few as ∼25% ′′ v ! 40 of the fields, but the large-scale component is present in *50% of them. The color distributions of the excess galaxy popular 2 K tions are indistinguishable from each other and are significantly redder than the color distribution of the field population, consistent with the excess being predominantly at . z 1 1 The magnitudes and colors of the excess galaxies are thus consistent with a population of predominantly early-type galaxies at the quasar redshifts, such as would be found in quasar host clusters or groups. Assuming that the excess galaxies are located at the quasar redshifts, the average excess within 0.5 Mpc (∼650) of the 21 h75 quasars corresponds to Abell richness class ∼ compared 0 5 1 to the galaxy surface density at more than 0.5 Mpc from 21 h 75 the quasars, and to Abell richness class ∼ compared 1.5 5 1.5 to the galaxy surface density from the literature. This suggests that on a large scale (*0.75 Mpc) RLQs at are 21 h z 5 1–2 75 located within clusters and/or large-scale galaxy structures of Abell richness ∼1, and that on a smaller scale (&0.5 Mpc) 21 h 75 within those structures RLQs can be located in unremarkable “field” environments or in groups or clusters up to Abell richness ∼0. For four fields with data in at least , I find that the spectral rJKs energy distributions (SEDs) of most of the excess galaxies are consistent with them being 2–3 Gyr old early-type galaxies at the quasar redshifts of , but that there are galaxies whose z ∼ 1.5 SEDs cannot be fitted by such simple models. Several objects have SEDs consistent with being 4–5 Gyr old at (Fig. z ∼ 1.5 1), and a number of others are consistent with old but dustreddened galaxies at the quasar redshifts. These potentially different galaxy types suggest that there is considerable dispersion in the properties of early-type cluster galaxies at z ∼ . Spectroscopic follow-up will be needed to confirm this 1.5 suggestion. In particular, age determinations from deep spectra of the candidate 4–5 Gyr old galaxies offer the possibility of constraining the cosmological model by requiring a relatively old universe at large lookback times. Lastly, there are a number of objects whose SEDs are best explained if they are background galaxies at . Many of z * 2.5 them seem to be dusty or to have composite stellar populations, or both, and some may be already *2 Gyr old at . z * 2.5

We have previously identified an excess population of predominantly red galaxies around a sample of 31 radio-loud quasars (RLQs) at 1 6) 2.7 times higher than the general field. Assuming these EROs are passively evolved galaxies at the quasar redshifts, they have characteristic luminosities of only ~L*. Only one of four RLQ fields has an excess of J-K?selected EROs with J-K > 2.5; thus, those objects are mostly unrelated to the quasars. We also present new multiwavelength data and analyses on the fields of four of these quasars at zq ~ 1.54, obtained to build more detailed pictures of the environments of these quasars and the galaxies within them. First, wide-field J and Ks data show that the galaxy excess around Q0835+580 is of Abell richness 2 ? 1 and extends to 140'' and that the galaxy excess around Q1126+101 extends to only 50'', even though the overall counts in the field are higher than the literature average. Second, in three fields we present the deepest narrowband redshifted H? observations yet published. We detect five candidate galaxies at the quasar redshifts, a surface density 2.5 times higher than in the only existing random-field survey of similar depth. However, photometric spectral energy distribution (SED) fitting of one candidate suggests that it is an [O III] detection background to the quasar. Third, SCUBA submillimeter observations of three fields detect two of the quasars and two galaxies with SEDs best fitted as highly reddened galaxies at the quasar redshifts. Fourth, H-band adaptive optics (AO) imaging is used to estimate redshifts for two moderately red bulge-dominated galaxies in the Q0835+580 field using the Kormendy relation between central surface brightness and half-light radius. Both have structural redshifts consistent with early-type galaxies foreground to the quasar at z 0.2 or 1 z 1.35. Photometric redshifts do not confirm these structural redshifts, however, possibly because our optical photometry for these objects is corrupted by scattered light from the nearby bright AO guide star. Finally, quantitative SED fits are presented for numerous galaxies of interest in two fields and are used to constrain their photometric redshifts, zph. Most galaxies in the spatially compact group around Q0835+580 are consistent with being at the quasar redshift zq. One of these is a candidate very old galaxy without ongoing star formation, while the others appear to have ongoing or recent star formation. Many very and extremely red objects across both fields have zph zq, and significant dust is required to fit most of them, including about half of the objects whose fits also require relatively old stellar populations. Large reddenings of E(B-V) 0.6 ? 0.3 are also required to fit four J-K-selected EROs in the Q1126+101 field, though all but one of them have best-fit redshifts zph > zq. These objects may represent a population of dusty high-redshift galaxies underrepresented in optically selected samples. Taken together, these observations reinforce the claim that radio-loud quasars at zq > 1 can be found in galaxy overdensities. Ongoing star formation with moderate amounts of dust seems to be common among all but the very reddest galaxies in these overdensities.

From direct imaging data, quantitative measures of the richness of the environment of quasars are derived using self-consistent galaxy luminosity function and galaxy count models. These models are obtained using the following procedure. By assuming that the excess galaxies found in the quasar fields are situated at the cosmological distance of the quasar redshifts and correcting for the background galaxy counts using control field counts, crude luminosity functions (LFs) of galaxies at three redshift bins centered at z = 0.24, 0.42, and 0.61 are determined for different values of q<SUB>0</SUB>. The absolute magnitudes of the excess galaxies are found to be consistent with that of galaxies at the cosmological redshift distances of the quasars. Using these measured LFs to estimate the evolution of galaxies and the current knowledge of the LF of local galaxies, self-consistent galaxy-count models are derived by comparing the computed galaxy counts with the control field galaxy counts. The best fitting models have q<SUB>0</SUB> = 0-0.5, depending on the adopted faint-end slope of the LF of local galaxies. The evolution of galaxies at z≍ 0.6 is equivalent to a brightening of 0.9 ± 0.5 mag for the best fitting models. However, because of the large statistical uncertainty in our background galaxy counts from a small total area, we can only constrain q<SUB>0</SUB> formally to be ≤ 1.5 at the 2 σ level. With these self-consistent world models, the quasar-galaxy covariance function is derived for samples of quasars having redshifts ranging from 0.05 to 0.65. The power-law slope of the covariance function is found to be entirely consistent with that of the galaxy-galaxy covariance function. Between z ≍ 0.4 and 0.6, there is an increase by a factor of ∼3 in the average quasar-galaxy covariance amplitude for radio-loud quasars. Some radio-loud quasars at z ≍ 0.6 are found in environments as rich as those of Abell class 1 clusters. This indicates that there has been significant evolution in the environments within some rich clusters over a time period of the order of one billion years, allowing them to support quasar activity at the earlier epoch. The apparent difference in the evolution time scale for quasars in different environments suggests that physical environmental conditions play a significant role in the evolution of quasars, implying that the evolution of the luminosity function of quasars cannot be entirely described by simple luminosity evolution models.

An optical photometric observation with the Beijing-Arizona-Taipei-Connecticut multicolor system is carried out for the central region of the nearby cluster of galaxies Abell 2634. From the 2K ? 2K CCD images with 14 filters, which cover a range of wavelength from 3600 to 10000 ?, 5572 sources are detected down to V ~ 20 mag in a field of 56' ? 56' centered on this regular cluster of galaxies. As a result, we achieved the spectral energy distributions (SEDs) of all sources detected. There are 178 previously known galaxies included in our observations, 147 of which have known radial velocities in the literature. After excluding the foreground and background galaxies, a sample of 124 known members is formed for an investigation of the SED properties. The comparison of observed SEDs of the early-type member galaxies with the template SEDs demonstrates the accuracy and reliability of our photometric measurements. Based on the knowledge of SED properties of member galaxies, we performed the selection of faint galaxies belonging to Abell 2634. It is well shown that the color-color diagrams are powerful in the star-galaxy separation. As a result, 359 faint galaxies are selected by their color features. The technique of photometric redshift and color-magnitude correlation for the early-type galaxies are applied for these faint galaxies, and a list of 74 faint member galaxies is achieved. On the basis of the newly generated sample of member galaxies, the spatial distribution and color-magnitude relation of the galaxies in the core region of Abell 2634 are discussed. There exists a tendency that the color index dispersion of the early-type members is larger for the outer region, which might reflect some clues about the environmental effect on the evolution of galaxies in a cluster.

Environmental differences in the stellar populations of early-type galaxies are explored using principal component analysis (PCA), focusing on differences between elliptical galaxies in Hickson Compact Groups (HCGs) and in the field. The method is model-independent and purely relies on variations between the observed spectra. The projections (PC1, PC2) of the observed spectra on the first and second principal components reveal a difference with respect to environment, with a wider range in PC1 and PC2 in the group sample. We define a spectral parameter (zeta equivalent to 0.36PC1 - PC2) which simplifies this result to a single number: field galaxies have a very similar value of zeta, whereas HCG galaxies span a wide range in this parameter. The segregation is found regardless of the way the input spectral energy distributions (SEDs) are presented to PCA (i.e. changing the spectral range; using uncalibrated data; subtracting the continuum or masking the SED to include only the Lick spectral regions). Simple models are applied to give physical meaning to the PCs. We obtain a strong correlation between the values of zeta and the mass fraction in younger stars, so that some group galaxies present a higher fraction of them, implying a more complex star formation history in groups. Regarding 'dynamically related' observables such as a(4) or velocity dispersion, we find a correlation with PC3, but not with either PC1 or PC2. PCA is more sensitive than other methods based on a direct analysis of observables such as the structure of the surface brightness profile or the equivalent width of absorption lines. The latter do not reveal any significant variation between field and compact group galaxies. Our results imply that the presence of young stars only amounts to a fraction of a per cent in its contribution to the total variance, reflecting the power of PCA as a tool to extract small variations in the spectra from unresolved stellar populations.

We study the galaxy environment of active galaxies, radio-loud and radio-quiet quasars in the redshift range 0.1 ≤ z ≤ 0.25. We use galaxies from the APM survey in order to explore the local galaxy overdensity and the b J - R colour distribution of neighbouring galaxies of these target samples. For comparison, we perform similar analysis on samples of Abell clusters with X-ray emission, and samples of Abell clusters with richness R = 1 and 0. The projected cross-correlations show that the samples of quasars and active galaxies reside in regions of galaxy density enhancements lower than those typical of R = 0 clusters. We also find that in the nearby Universe the local galaxy overdensities of radio-loud and radio-quiet quasars are comparable. The analysis of the distribution of b J - R galaxy colour indices suggests that the environment of quasars is not strongly dominated by a population of red galaxies, characteristic of rich Abell clusters, an effect that is more clearly appreciated for our sample of radio-loud quasars.

<i>Aims. <i/>We investigate the dependence of several galaxy properties on the environment and cluster identification techniques.<i>Methods. <i/>We select clusters of galaxies from two catalogues based on the SDSS: the ROSAT-SDSS galaxy cluster survey, which is an X-ray selected cluster sample and the MaxBCG catalogue, in which clusters are optically selected. Based on a volume limited sample of galaxies drawn from the spectroscopic DR5 SDSS, we constructed sub-samples of clusters of galaxies with more than ten members. Scaling relations as well as segregation of galaxy properties as a function of the normalized clustocentric radii are analyzed. The properties of galaxies in clusters are compared with those of field galaxies.<i>Results. <i/>Galaxies in X-ray and MaxBCG selected clusters show similar size-luminosity relations. At equal luminosity, late type galaxies in the field have sizes smaller than cluster galaxies of the same morphological type. The Faber-Jackson relation for early-type galaxies in clusters is also the same for X-ray selected and MaxBCG clusters. We found clear differences between the dynamical properties of galaxies in clusters, the brightest cluster galaxies (<i>BCG<i/><sub>s<sub/>) and field galaxies. Using several criteria to classify galaxies into morphological types, we reproduce the well know morphological segregation. The correlation is up to . For the whole range of clustocentric distances, X-ray selected clusters present a higher fraction of early type galaxies than MaxBCG clusters. We also found that bright galaxies preferentially inhabit the cluster centers. Median sizes of galaxies, such as the radius that encloses of Petrosian flux <i>r<i/><sub>50<sub/>, present a behaviour that also depends on the cluster selection criteria. For galaxies in X-ray selected clusters, median values of <i>r<i/><sub>50<sub/> decrease as goes to zero, whereas the opposite is observed for galaxies in the MaxBCG clusters. These different behaviours are mainly due to early type galaxies. The results are discussed in terms of the different processes that affect the evolution of galaxies in different environments.

Aims. We study differences in the physical properties of quasar host galaxies using an optically selected sample of radio-loud (RL) and radio-quiet quasars (in the redshift range 0.15 ≤ z ≤ 1.9) that we have further cross-matched with the VLA-FIRST survey catalogue. The sources in our sample have broad Hβ and Mg II emission lines (1000 km/s &lt; FWHM &lt; 15 000 km/s) with a sub-sample of high broad-line quasars (FWHM &gt; 15 000 km/s). We constructed the broad-band spectral energy distribution (SED) of our broad-line quasars using multi-wavelength archival data and targeted observations with the AstroSat telescope. Methods. We used the state-of-the-art SED modelling code CIGALE v2022.0 to model the SEDs and determine the best-fit physical parameters of the quasar host galaxies; namely, their star formation rate (SFR), main-sequence stellar mass, luminosity absorbed by dust, e-folding time, and stellar population age. Results. We find that the emission from the host galaxy of our sources is between 20% and 35% of the total luminosity, as they are mostly dominated by central quasars. Using the best-fit estimates, we reconstructed the optical spectra of our quasars, which show remarkable agreement in reproducing the observed SDSS spectra of the same sources. We plot the main-sequence relation for our quasars and note that they are significantly away from the main sequence of star-forming galaxies. Further, the main-sequence relation shows a bimodality for our RL quasars, indicating populations segregated by Eddington ratios. Conclusions. We conclude that RL quasars in our sample with lower Eddington ratios tend to have substantially lower SFRs for similar stellar mass. Our analyses thus provide a completely independent route to studying the host galaxies of quasars and addressing the radio dichotomy problem from the host galaxy angle.

The spectral energy distribution (SED) of galaxies varies both between galaxies and within them. For instance, early-type spiral galaxies have a red bulge surrounded by a bluer star-forming disk with H II regions within. When observing redshifted galaxies, a given photometric filter probes light at a bluer rest frame, and in relating the observed magnitudes to the rest frame of the filter, so-called k corrections are commonly applied to account for the relative dimming or brightening in addition to the pure distance effect. The amount of correction depends on the shape of the spectrum (SED), so different k corrections apply to galaxies of different spectral types. This is, however, only part of the story, since any galaxy with a spatially non-homogeneous SED will experience a spatially varying relative dimming or brightening as a function of observed wavelength. Also, the morphological appearance of galaxies will therefore change with redshift. For instance, an early spiral galaxy observed in the V band would show a prominent bulge at z = 0, whereas, if at redshift z ∼ 1, the V filter probes emission in the rest-frame near-ultraviolet where the bulge is faint and the disk relatively brighter, thus the galaxy may appear as bulgeless. One popular way of studying spatial variations in the stellar population and dust content of galaxies is the use of color maps. For star-forming galaxies that have an appreciable contribution from nebular emission (lines and continuum), an additional effect is that the shifting of strong features in or out of filters will result in a non-monotonous color evolution with redshift. Hence, unlike the effects of distance, cosmological surface brightness dimming, and gravitational lensing, which are all achromatic, the fact that most galaxies have a spatially varying SED leads to a chromatic surface brightness modulation (CMOD) with redshift. While the CMOD effects are in principle easy to grasp, they affect multicolor imaging surveys and photometric properties derived from such surveys in a complex fashion. Properties such as the bulge-to-disk ratio, Sérsic exponent, light concentration, asymmetry index and effective radius, radial color gradients, and stellar mass determinations from SED fitting will depend on the redshift, the filters employed, and the rest-frame 2D SED patterns in a galaxy and will bias results inferred on galaxy evolution across cosmic time (e.g., the evolution of the mass-size, bulge-supermassive black hole, and Tully-Fisher relation), and potentially also weak lensing, if these effects are not properly taken into account. In this article we quantify the CMOD effects for idealized galaxies built from spectral synthesis models and from galaxies with observed integral field spectroscopy, and we show that they are significant and should be taken into account in studies of resolved galaxy properties and their evolution with redshift.

We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) data on the large-scale environments of 16 0.39 < z < 0.51 quasars from the Large Bright Quasar Survey (LBQS). The LBQS quasars are representative of the radio-quiet population, and this is one of the first looks at their large-scale environments. We compare the LBQS environments with the environments of 27 0.15 < z < 0.55 quasars selected from the HST archive. The majority of the Archive quasars are from the PG and PKS surveys, and these quasars are more luminous on average than the LBQS. By comparing the LBQS and Archive environments, we investigate whether previous quasar environment studies have been biased as a result of studying unusually radio or optically luminous quasars. We compare observed galaxy number counts with expected counts predicted from the CNOC2 field galaxy luminosity function in order to look for statistical excesses of galaxies around the quasars. We detect a significant excess around the Archive quasars but find no such excess around the LBQS quasars. We calculate the amplitude of the spatial correlation function and find that the LBQS environments are consistent with that of the typical galaxy while the Archive environments are slightly less rich than Abell 0 clusters. We find no difference between the environments of radio-loud and radio-quiet quasars in either sample. However, comparison with previously published work shows that the LBQS radio-loud quasars are in sparse environments when compared with other radio-loud quasars, and the Archive radio-quiet quasars are in dense environments compared to other radio-quiet quasars. The richer environments of the Archive radio-quiet quasars cannot be explained by their higher optical luminosities. We find a positive correlation (95%) between radio luminosity and environment for the radio-loud quasars. This may explain why the LBQS radio-loud quasars, which are less radio luminous, are in sparser environments.

This thesis presents results from the deepest ever far-infrared study of the Coma cluster (Abell 1656), with the Herschel PACS and SPIRE instruments being used to observe the cluster at a wavelength range of 70-500 _m. These observations resulted in a catalogue consisting of 70 galaxies which were spectroscopically confirmed as Coma cluster members, from which far-infrared galaxy luminosity functions at 70, 100 and 160 _m were constructed. Additionally, the far-infrared properties of 68 of these galaxies were determined from spectral energy distribution fits across the full wavelength range. Finally, these galaxies were grouped by morphological type, resulting in 30 elliptical galaxies, 37 spiral galaxies and one with an unknown morphology. These results were then compared to other studies of both clusters and the field in order to ascertain the extent to which environmental processes affect galaxy evolution. A comparison of the luminosity functions at 100 and 160 _m and the equivalent functions from the Herschel Virgo cluster survey Auld et al. (2013) showed similarities in both the functional form and the function parameters describing them. A further comparison of the Coma cluster luminosity functions at all three PACS wavelengths and various field galaxy luminosity functions was made, and again the forms and function parameters were consistent to within the errors. This would imply that the environmental processes thought to occur within the clusters do not have as great an effect on the galaxy population as initially thought. The far-infrared properties derived from the spectral energy distribution fits were analysed by galaxy type. The early-types were found to have mean normalised dust masses, dust temperatures and total infrared luminosities of log10 _ Mdust Mstellar =

We introduce a framework for simultaneously investigating the structure and luminosity evolution of early-type gravitational lens galaxies. The method is based on the fundamental plane, which we interpret using the aperture mass-radius relations derived from lensed image geometries. We apply this method to our previous sample of 22 lens galaxies with measured redshifts and excellent photometry. Modeling the population with a single mass profile and evolutionary history, we find that early-type galaxies are nearly isothermal (logarithmic density slope n = 2.06 +/- 0.17, 68% C.L.), and that their stars evolve at a rate of dlog(M/L)_B/dz = -0.50 +/- 0.19 (68% C.L.) in the rest frame B band. For a Salpeter IMF and a concordance cosmology, this implies a mean star formation redshift of > 1.5 at 95% confidence. While this model can neatly describe the mean properties of early-type galaxies, it is clear that the scatter of the lens sample is too large to be explained by observational uncertainties alone. We therefore consider statistical models in which the galaxy population is described by a distribution of star formation redshifts. We find that stars must form over a significant range of redshifts (Delta z_f > 1.7, 68% C.L.), which can extend as low as z_f = 1 for some acceptable models. However, the typical galaxy will still have an old stellar population ( > 1.5). The lens sample therefore favors early star formation in field ellipticals -- even if we make no a priori assumption regarding the shape of the mass distribution in lenses, and include the range of possible deviations from homology in the uncertainties. Our evolution results call into question several recent claims that early-type galaxies in low-density environments have much younger stars than those in rich clusters.

We perform a comparison of the properties of galaxies in compact groups, loose groups and in the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. We select samples of galaxies in compact groups identified by McConnachie et al., loose groups identified by Zandivarez and Martinez, and field galaxies from the Sloan Digital Sky Survey. We compare properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass and concentration. We also study the fraction of red and early type galaxies, the luminosity function, the colour-luminosity and luminosity-size relations. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of read and early type galaxies is higher in compact groups. On average, galaxies in compact groups are systematically smaller, more concentrated and have higher surface brightness than galaxies in the field and in loose groups. For fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups given the high densities and low velocity dispersion that characterise that particular environment, this could explain the large fraction of red and early type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.

Multi-Wavelength Properties of Submillimeter-Selected Galaxies

This paper presents theoretical integrated spectral energy distributions (SEDs) of binary star composite stellar populations (bsCSPs) in early-type galaxies, and how the bsCSP model can be used for spectral studies of galaxies. All bsCSPs are built basing on three adjustable inputs (metallicity, ages of old and young components). The effects of binary interactions and stellar population mixture are taken into account. The results show some UV-upturn SEDs naturally for bsCSPs. The SEDs of bsCSPs are affected obviously by all of three stellar population parameters, and the effects of three parameters are degenerate. This suggests that the effects of metallicity, and the ages of the old (major in stellar mass) and young (minor) components of stellar populations should be taken into account in SED studies of early-type galaxies. The sensitivities of SEDs at different wavelengths to the inputs of a stellar population model are also investigated. It is shown that UV SEDs are sensitive to all of three stellar population parameters, rather than to only stellar age. Special wavelength ranges according to some SED features that are relatively sensitive to stellar metallicity, young-component age, and old-component age of bsCSPs are found by this work. For example, the shapes of SEDs with wavelength ranges of 5110-5250AA, 5250--5310AA, 5310--5350AA, 5830--5970AA, 20950--23550AA are relatively sensitive to the stellar metallicity of bsCSPs. The shapes of SEDs within 965-985AA, 1005--1055AA, 1205--1245AA are sensitive to old-component age, while SED features within the wavelength ranges of 2185--2245AA, 2455--2505AA, 2505--2555AA, 2775--2825AA, 2825--2875AA to young-component age.