ABSTRACT
We present spectra and near-infrared images of a sample of faint radio sources initially selected as promising high-redshift radio galaxy (HzRG) candidates. We have determined redshifts for ...a total of 13 radio galaxies with redshifts ranging from 0.52 ≤ $z$ ≤ 5.72. Our sample probes radio luminosities that are almost an order of magnitude fainter than previous large samples at the highest redshifts. We use near-infrared photometry for a subsample of these galaxies to calculate stellar masses using simple stellar population models, and find stellar masses to be in the range $10^{10.8} {--}10^{11.7} \, \mathrm{M}_\odot$. We then compare our faint radio galaxies with brighter radio galaxies at $z$ ≥ 2 from the literature. We find that fainter radio galaxies have lower Ly α luminosities and narrower line widths compared to the bright ones, implying photoionization by a weaker active galactic nucleus (AGN). We also rule out the presence of strong shocks in faint HzRGs. The stellar masses determined for faint HzRGs are lower than those observed for brighter ones. We find that faint HzRG population in the redshift range 2–4 forms a bridge between star-forming and narrow-line AGNs, whereas the ones at $z$ > 4 are likely to be dominated by star formation, and may be building up their stellar mass through cold accretion of gas. Finally, we show that the overall redshift evolution of radio sizes at $z$ > 2 is fully compatible with increased inverse Compton scattering losses at high redshifts.
We present the first systematic study of the stellar populations of ultra-diffuse galaxies (UDGs) in the field, integrating the large area search and characterization of UDGs by the SMUDGes survey ...with the twelve-band optical photometry of the S-PLUS survey. Based on Bayesian modeling of the optical colors of UDGs, we determine the ages, metallicities, and stellar masses of 100 UDGs distributed in an area of ∼330 deg2 in the Stripe 82 region. We find that the stellar masses and metallicities of field UDGs are similar to those observed in clusters and follow the trends previously defined in studies of dwarf and giant galaxies. However, field UDGs have younger luminosity-weighted ages than do UDGs in clusters. We interpret this result to mean that field UDGs have more extended star formation histories, including some that continue to form stars at low levels to the present time. Finally, we examine stellar population scaling relations that show that UDGs are, as a population, similar to other low surface brightness galaxies.
We have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (L sub(Ly) alpha approximately 10 ...super(44) erg s super(-1)) and nearest (z approximately 2.38) of all Ly alpha blobs (LABs). The dominant optical emission line component shows relatively broadlines (600-800 km s super(-1), FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Ly alpha in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment.
ABSTRACT
We present Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI) observations of 35 quasars at 2.1 < z < 3.2, the majority of which were ...selected from the Clusters Around Radio-Loud AGN (CARLA) survey. CARLA quasars have large C iv-based black hole masses (MBH > 109 M⊙) and powerful radio emission ($P_{500\, \rm MHz}$ > 27.5 W Hz−1). We estimate H α-based MBH, finding a scatter of 0.35 dex compared to C iv. We evaluate several recipes for correcting C iv-based masses, which reduce the scatter to 0.24 dex. The radio power of the radio-loud quasars is at most weakly correlated with the interconnected quantities H αwidth, L5100, and MBH, suggesting that it is governed by different physical processes. However, we do find a strong inverse correlation between C iv blueshift and radio power linked to higher Eddington ratios and L5100. Under standard assumptions, the black hole (BH) growth time is longer than the cosmic age for many CARLA quasars, suggesting that they must have experienced more efficient growth in the past. If these BHs were growing from seeds since the epoch of reionization, it is possible that they grew at the Eddington limit like the quasars at z ∼ 6–7, and then continued to grow at the reduced rates observed until z ∼ 2–3. Finally, we study the relation between MBH and environment, finding a weak positive correlation between MBH and galaxydensity measured by CARLA.
Discovery of a radio galaxy at z = 5.72 Saxena, A; Marinello, M; Overzier, R A ...
Monthly notices of the Royal Astronomical Society,
10/2018, Letnik:
480, Številka:
2
Journal Article
Abstract
We present a detailed study of the kinematic, chemical and excitation properties of the giant Ly α emitting nebula and the giant H i absorber associated with the z = 2.92 radio galaxy MRC ...0943–242, using spectroscopic observations from Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE), VLT/X-SHOOTER and other instruments. Together, these data provide a wide range of rest-frame wavelength (765–6378 Å at z = 2.92) and 2D spatial information. We find clear evidence for jet gas interactions affecting the kinematic properties of the nebula, with evidence for both outflows and inflows being induced by radio-mode feedback. We suggest that the regions of relatively lower ionization level, spatially correlated with the radio hotspots, may be due to localized compression of photoionized gas by the expanding radio source, thereby lowering the ionization parameter, or due to a contribution from shock-heating. We find that photoionization of supersolar metallicity gas (Z/Z⊙ = 2.1) by an active galactic nuclei-like continuum (α = −1.0) at a moderate ionization parameter (U = 0.018) gives the best overall fit to the complete X-SHOOTER emission-line spectrum. We identify a strong degeneracy between column density and Doppler parameter such that it is possible to obtain a reasonable fit to the H i absorption feature across the range log N(H i/cm−2) = 15.20 and 19.63, with the two best fitting occurring near the extreme ends of this range. The extended H i absorber is blueshifted relative to the emission-line gas, but shows a systematic decrease in blueshift towards larger radii, consistent with a large-scale expanding shell.
We present the results of a large program conducted with the Very Large Telescope and augmented by observations with the Keck telescope to search for forming clusters of galaxies near powerful radio ...galaxies at 2.0 < z < 5.2. Besides MRC 1138-262 at z = 2.16, the radio galaxy observed in our pilot program, we obtained narrow- and broad-band images of eight radio galaxies and their surroundings. The imaging was used to select candidate Ly\alpha emitting galaxies in 3\times3 Mpc super(2) areas near the radio galaxies. A total of 300 candidate emitters were found with a rest-frame Ly\alpha equivalent width of EW sub(0) > 15 Aa and significance 3$--> \Sigma \equiv {\it EW}_0/\Delta {\it EW}_0 > 3. Follow-up spectroscopy was performed on 152 candidates in seven of the radio galaxy fields. Of these, 139 were confirmed to be Ly\alpha emitters, four were low redshift interlopers and nine were non-detections. With the adopted criteria the success rate is 139/152 = 91%. In addition, 14 objects with EW sub(0) < 15 and/or \Sigma < 3 were confirmed to be Ly\alpha emitters. Combined with the 15 Ly\alpha emitters near MRC 1138-262, we have determined Ly\alpha redshifts for 168 objects near eight radio galaxies. At least six of our eight fields are overdense in Ly\alpha emitters by a factor 3-5 as compared to the field density of Ly\alpha emitters at similar redshifts, although the statistics in our highest redshift field ( z = 5.2) are poor. Also, the emitters show significant clustering in velocity space. In the overdense fields, the width of the velocity distributions of the emitters is a factor 2-5 smaller than the width of the narrow-band filters. Taken together, we conclude that we have discovered six forming clusters of galaxies (protoclusters). We estimate that roughly 75% of powerful ( 10 logical and --> L_\mathrm > 10erg s super(-1) Hz super(-1) sr super(-1)) high redshift radio galaxies reside in a protocluster. The protoclusters have sizes of at least 1.75 Mpc, which is consistent with the structure sizes found by other groups. By using the volume occupied by the overdensities and assuming a bias parameter of b =3-6, we estimate that the protoclusters have masses in the range 2{-}9 \times 10M_{\odot}. These protoclusters are likely to be progenitors of present-day (massive) clusters of galaxies. For the first time, we have been able to estimate the velocity dispersion of cluster progenitors from z\sim5 to similar to 2. The velocity dispersion of the emitters increases with cosmic time, in agreement with the dark matter velocity dispersion in numerical simulations of forming massive clusters.
The environment of the high-z radio galaxy PKS 1138−262 at z∼ 2.2 is a prime example of a forming galaxy cluster. We use deep Spectrograph for INtegral Field Observations in the Near Infrared ...(SINFONI) integral field spectroscopy to perform a detailed study of the kinematics of the galaxies within 60 kpc of the radio core and we link this to the kinematics of the protocluster on the megaparsec scale. Identification of optical emission lines shows that 11 galaxies are at the redshift of the protocluster. The density of line emitters is more than an order of magnitude higher in the core of the protocluster with respect to the larger scale environment. This implies a galaxy overdensity in the core of δg∼ 200 and a matter overdensity of δm∼ 70; the latter is similar to that of the outskirts of local galaxy clusters. The velocity distribution of the confirmed satellite galaxies shows a broad, double-peaked velocity structure with σ= 1360 ± 206 km s−1. A similar broad, double-peaked distribution was found in a previous study targeting the large-scale protocluster structure, indicating that a common process is acting on both small and large scales. Including all spectroscopically confirmed protocluster galaxies, a velocity dispersion of 1013 ± 87 km s−1 is found. We show that the protocluster has likely decoupled from the Hubble flow and is a dynamically evolved structure. A comparison to the Millennium Simulation indicates that the protocluster velocity distribution is consistent with that of the most massive haloes at z∼ 2, but we rule out that the protocluster is a fully virialized structure based on dynamical arguments and its X-ray luminosity. Comparison to merging haloes in the Millennium Simulation shows that the structure as observed in and around the Spiderweb galaxy is best interpreted as being the result of a merger between two massive haloes. We propose that the merger of two subclusters can result in an increase in star formation and active galactic nucleus activity in the protocluster core, therefore possibly being an important stage in the evolution of massive cD galaxies.
Previous work has shown that Lyman break galaxies (LBGs) display a range in structures (from single and compact to more clumpy and extended) that is different from typical local star-forming ...galaxies. Recently, we have introduced a sample of rare, nearby (z < 0.3) starburst galaxies that appear to be good analogs of LBGs. These 'Lyman break analogs' (LBAs) provide an excellent training set for understanding starbursts at different redshifts. We present an application of this by comparing the rest-frame ultraviolet (UV) and optical morphologies of 30 LBAs with those of galaxies at z {approx} 2-4 in the Hubble Ultra Deep Field. We compare LBAs with star-forming sBzK galaxies at z {approx} 2, and LBGs at z {approx} 3-4 at the same intrinsic UV luminosity (L{sub UV} {approx}> 0.3L*{sub z=3}). The UV/optical colors and sizes of LBAs and LBGs are very similar, while the BzK galaxies are somewhat redder and larger. LBAs lie along a mass-metallicity relation that is offset from that of typical local galaxies, but similar to that seen at z {approx} 2. There is significant overlap between the morphologies (G, C, A, and M{sub 20}) of the local and high-redshift samples, although the high-redshift samples are somewhat less concentrated and clumpier than the LBAs. Based on their highly asymmetric morphologies, we find that in the majority of LBAs the starbursts appear to be triggered by interactions/mergers. When the images of the LBAs are degraded to the same sensitivity and linear resolution as the images of LBGs and BzK galaxies, we find that these relatively faint asymmetric features are no longer detectable. This effect is particularly severe in the rest-frame UV. It has been suggested that high-redshift galaxies experience intense bursts unlike anything seen in the local universe, possibly due to cold flows and instabilities. In part, this is based on the fact that the majority ({approx}70%) of LBGs do not show morphological signatures of interactions or mergers. Our results suggest that this evidence is insufficient, since a large fraction of such signatures would likely have been missed in current observations of galaxies at z {approx} 2-4. This leaves open the possibility that clumpy accretion and mergers remain important in driving the evolution of these starbursts, together with rapid gas accretion through other means.
ABSTRACT
This paper provides a catalogue of stars, quasars, and galaxies for the Southern Photometric Local Universe Survey Data Release 2 (S-PLUS DR2) in the Stripe 82 region. We show that a 12-band ...filter system (5 Sloan-like and 7 narrow bands) allows better performance for object classification than the usual analysis based solely on broad bands (regardless of infrared information). Moreover, we show that our classification is robust against missing values. Using spectroscopically confirmed sources retrieved from the Sloan Digital Sky Survey DR16 and DR14Q, we train a random forest classifier with the 12 S-PLUS magnitudes + 4 morphological features. A second random forest classifier is trained with the addition of the W1 (3.4 $\mu\mathrm{m} $) and W2 (4.6 $\mu\mathrm{m} $) magnitudes from the Wide-field Infrared Survey Explorer (WISE). Forty-four per cent of our catalogue have WISE counterparts and are provided with classification from both models. We achieve 95.76 per cent (52.47 per cent) of quasar purity, 95.88 per cent (92.24 per cent) of quasar completeness, 99.44 per cent (98.17 per cent) of star purity, 98.22 per cent (78.56 per cent) of star completeness, 98.04 per cent (81.39 per cent) of galaxy purity, and 98.8 per cent (85.37 per cent) of galaxy completeness for the first (second) classifier, for which the metrics were calculated on objects with (without) WISE counterpart. A total of 2926 787 objects that are not in our spectroscopic sample were labelled, obtaining 335 956 quasars, 1347 340 stars, and 1243 391 galaxies. From those, 7.4 per cent, 76.0 per cent, and 58.4 per cent were classified with probabilities above 80 per cent. The catalogue with classification and probabilities for Stripe 82 S-PLUS DR2 is available for download.
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