Rest-frame Ultraviolet Continuum Research Articles

Big Three Dragons: Molecular Gas in a Bright Lyman-break Galaxy at z = 7.15

We report Atacama Large Millimeter/submillimeter Array Band 3 observations of CO(6−5), CO(7−6), and [C i](2−1) in B14-65666 (“Big Three Dragons”), one of the brightest Lyman-break galaxies at z > 7 in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of [O iii] 88 μm and [C ii] 158 μm. CO(6−5), CO(7−6), and [C i](2−1), whose 3σ upper limits on the luminosities are approximately 40 times fainter than the [C ii] luminosity, are all not detected. The L [C II]/L CO(6–5) and L [C II]/L CO(7–6) ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) [C ii] luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass (M mol) is (0.05–11) × 1010 M ⊙. This value is consistent with the upper limit inferred from the nondetection of mid-J CO and [C i](2−1). Despite the large uncertainty in M mol, we estimate a molecular gas-to-stellar mass ratio (μ gas) of 0.65–140 and a gas depletion time (τ dep) of 2.5–550 Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at z ≳ 4 if no gas is fueled from outside the galaxy.

The ultraviolet continuum slopes (β) of galaxies at z ≃ 8-16 from JWST and ground-based near-infrared imaging

ABSTRACT We study the rest-frame ultraviolet (UV) continuum slopes (β) of galaxies at redshifts 8 < z < 16 (〈z〉 = 10), using a combination of JWST ERO and ERS NIRCam imaging and ground-based near-infrared imaging of the COSMOS field. The combination of JWST and ground-based imaging provides a wide baseline in both redshift and absolute UV magnitude (−22.6 < MUV < −17.9), sufficient to allow a meaningful comparison to previous results at lower redshift. Using a power-law fitting technique, we find that our full sample (median MUV = −19.3 ± 1.3) returns an inverse-variance weighted mean value of 〈β〉 = −2.10 ± 0.05, with a corresponding median value of β = −2.29 ± 0.09. These values imply that the UV colours of galaxies at z > 8 are, on average, no bluer than the bluest galaxies in the local universe (e.g. NGC 1705; β = −2.46). We find evidence for a β − MUV relation, such that brighter UV galaxies display redder UV slopes ($\rm {d}\beta / \rm {d} M_{\rm UV} = -0.17 \pm 0.05$). Comparing to results at lower redshift, we find that the slope of our β − MUV relation is consistent with the slope observed at z ≃ 5 and that, at a given MUV, our 8 < z < 16 galaxies are bluer than their z ≃ 5 counterparts, with an inverse-variance weighted mean offset of 〈Δβ〉 = −0.38 ± 0.09. We do not find strong evidence that any objects in our sample display ultra-blue UV continuum slopes (i.e. β ≲ −3) that would require their UV emission to be dominated by ultra-young, dust-free stellar populations with high Lyman-continuum escape fractions. Comparing our results to the predictions of theoretical galaxy formation models, we find that the galaxies in our sample are consistent with the young, metal-poor, and moderately dust-reddened galaxies expected at z > 8.

ALMA Reveals Extended Cool Gas and Hot Ionized Outflows in a Typical Star-forming Galaxy at Z = 7.13

We present spatially resolved morphological properties of [C II] 158 μm, [O III] 88 μm, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* galaxy at z = 7.13, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the [O III] line and UV continuum are compact, the [C II] line is extended up to a radius of r ∼ 12 kpc. Using multi-band rest-frame far-infrared continuum data ranging from 52 to 400 μm, we find an average dust temperature and emissivity index of K and , respectively, across the galaxy. We find slight differences in the dust continuum profiles at different wavelengths, which may indicate that the dust temperature decreases with distance. We map the star formation rate (SFR) via IR and UV luminosities and determine a total SFR of 37 ± 1M ⊙yr−1 with an obscured fraction of 87%. While the [O III] line is a good tracer of the SFR, the [C II] line shows deviation from the local L [C II]-SFR relations in the outskirts of the galaxy. Finally, we observe a clear difference in the line profile between [C II] and [O III], with significant residuals (∼5σ) in the [O III] line spectrum after subtracting a single Gaussian model. This suggests a possible origin of the extended [C II] structure from the cooling of hot ionized outflows. The extended [C II] and high-velocity [O III] emission may both contribute in part to the high L [O III]/L [C II] ratios recently reported in z > 6 galaxies.

The ALPINE–ALMA [C ii] Survey: Size of Individual Star-forming Galaxies at z = 4–6 and Their Extended Halo Structure

Abstract We present the physical extent of [C ii] 158 μm line-emitting gas from 46 star-forming galaxies at z = 4–6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C ii] line ( ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum ( ) from Hubble Space Telescope images. The effective radius exceeds by factors of ∼2–3, and the ratio of increases as a function of M star. We do not find strong evidence that the [C ii] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ≃1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C ii] component over 10 kpc scales detected at 4.1σ–10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C ii]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C ii] line structure have high star formation rate, high stellar mass (M star), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C ii] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C ii] line structures are ubiquitous to high-z star-forming galaxies.

Spatially separated continuum sources revealed by microlensing in the gravitationally lensed broad absorption line quasar SDSS J081830.46+060138.0

Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 (J0818+0601) at redshift z ≃ 2.35. We first show that J0818+0601 is actually gravitationally lensed, and not a binary quasar. A strong absorption system detected at z = 1.0065 ± 0.0002 is possibly due to the lensing galaxy. Microlensing is observed in one image and it magnifies the emission lines, the continuum, and the BALs differently. By disentangling the part of the spectrum that is microlensed from the part that is not microlensed, we unveil two sources of continuum that must be spatially separated: a compact one, which is microlensed, and an extended one, which is not microlensed and contributes to two thirds of the total continuum emission. J0818+0601 is the second BAL quasar in which an extended source of rest-frame ultraviolet continuum is found. We also find that the images are differently polarized, suggesting that the two continua might be differently polarized. Our analysis provides constraints on the BAL flow. In particular, we find that the outflow is seen with a nonzero onset velocity, and stratified according to ionization.

Active and dust obscured star-forming galaxies at z ∼ 4 probed with UV spectral slope beta

AbstractWe investigate the stellar population of star-forming galaxies at z ∼ 4 by focusing on their slope of rest-frame ultraviolet continuum called UV spectral slope β. We analyze the sample of bright Lyman Break Galaxies (LBGs) with Subaru/i′≤26.0in the Subaru/XMM-Newton Deep Survey field. Our detailed SED fitting analysis indicates that the LBGs with observed UV slope > −1.7, , Av > 1.0, and intrinsic UV slope < −2.5 are the intrinsically active star-forming galaxies with star formation rates larger than a few × 102 M⊙yr−1. A significant fraction of the UV-selected LBGs at z ∼ 4 is on-going active and dust obscured star-forming galaxies.

The UV spectral slope β and stellar population of most active star-forming galaxies at z ∼ 4

Abstract We investigate a stellar population of star-forming galaxies at z ∼ 4 by focusing on the slope of their rest-frame ultraviolet (UV) continuum, β, where fλ ∝ λβ. We investigate a sample of bright Lyman break galaxies (LBGs) with i′ ≤ 26.0 in the Subaru/XMM-Newton Deep Survey field by using a spectral energy distribution fitting analysis. We find that the apparently redder (βobs > −1.73) LBGs tend to be dusty (AV > 1.0), and have young stellar populations (βint < −2.42) and intrinsically active star-forming galaxies (SFR ≳ a few $\times \ 10^{2}\, {M_{\odot }}\:\mbox{yr}^{-1}$). This means that a significant fraction of the UV-selected LBGs at z ∼ 4 contains on-going, active, and dust-obscured star-forming galaxies. We compare the infrared to UV luminosity ratio, which is estimated from our optical/near-infrared data assuming dust attenuation laws, with sub-millimeter observations from previous works. The result suggests that the Calzetti-like dust attenuation law is preferable for active and dusty star-forming LBGs at z = 4. We also find that an extrapolation of the βint–MUV, int relation toward the fainter magnitude range below our sample magnitude limit intersects the βobs–MUV, obs relation previously obtained in deeper narrow-area observations at MUV = −18.9 and β = −1.94, which coincides with the break point of the βobs–MUV, obs relation observed so far. This coincidence suggests that we see an almost dust-free population at MUV, obs ≳ −18.9.

The BOSS Emission-line Lens Survey. V. Morphology and Substructure of Lensed Lyα Emitters at Redshift Z ≈ 2.5 in the BELLS GALLERY

Abstract We present a morphological study of the 17 lensed Lyα emitter (LAE) galaxies of the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) for the GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) sample. This analysis combines the magnification effect of strong galaxy–galaxy lensing with the high resolution of the Hubble Space Telescope to achieve a physical resolution of ∼80 pc for this 2 < z < 3 LAE sample, allowing a detailed characterization of the LAE rest-frame ultraviolet continuum surface brightness profiles and substructure. We use lens-model reconstructions of the LAEs to identify and model individual clumps, which we subsequently use to constrain the parameters of a generative statistical model of the LAE population. Since the BELLS GALLERY sample is selected primarily on the basis of Lyα emission, the LAEs that we study here are likely to be directly comparable to those selected in wide-field, narrowband LAE surveys, in contrast with the lensed LAEs identified in cluster-lensing fields. We find an LAE clumpiness fraction of approximately 88%, which is significantly higher than that found in previous (non-lensing) studies. We find a well-resolved characteristic clump half-light radii of ∼350 pc, a scale comparable to the largest H ii regions seen in the local universe. This statistical characterization of LAE surface-brightness profiles will be incorporated into future lensing analyses using the BELLS GALLERY sample to constrain the incidence of dark-matter substructure in the foreground lensing galaxies.

Spatially Resolved Patchy Lyα Emission within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8

Abstract We report the detection of extended Lyα emission from the host galaxy of SDSS J2222+2745, a strongly lensed quasar at z = 2.8. Spectroscopic follow-up clearly reveals extended Lyα in emission between two images of the central active galactic nucleus (AGN). We reconstruct the lensed quasar host galaxy in the source plane by applying a strong lens model to HST imaging and resolve spatial scales as small as ∼200 pc. In the source plane, we recover the host galaxy morphology to within a few hundred parsecs of the central AGN and map the extended Lyα emission to its physical origin on one side of the host galaxy at radii ∼0.5–2 kpc from the central AGN. There are clear morphological differences between the Lyα and rest-frame ultraviolet stellar continuum emission from the quasar host galaxy. Furthermore, the relative velocity profiles of quasar Lyα, host galaxy Lyα, and metal lines in outflowing gas reveal differences in the absorbing material affecting the AGN and host galaxy. These data indicate the presence of patchy local intervening gas in front of the central quasar and its host galaxy. This interpretation is consistent with the central luminous quasar being obscured across a substantial fraction of its surrounding solid angle, resulting in strong anisotropy in the exposure of the host galaxy to ionizing radiation from the AGN. This work demonstrates the power of strong-lensing-assisted studies to probe spatial scales that are currently inaccessible by other means.

DISCOVERY OF A FAINT QUASAR AT z ∼ 6 AND IMPLICATIONS FOR COSMIC REIONIZATION

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ($M_{1450}>-24$ mag) at $z \gtrsim6$, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z~6 in a 12.5 deg$^{2}$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at $\sim8443~\rm{\AA}$, with emission lines redshifted to $z=5.944 \pm 0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59\pm0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars . This suggests that the number of $M_{1450}\sim-23$ mag quasars at z~6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.

Dynamics and metallicity of far-infrared selected galaxies

We present near-infrared integral field spectroscopy of ten Herschel selected galaxies at z~1.5. From detailed mapping of the H$\alpha$ and [NII] emission lines we trace the dynamics, star formation rates, metallicities and also investigate gas fractions for these galaxies. For a few galaxies the distribution of star formation as traced by H$\alpha$ only traces a small fraction of the stellar disc, which could be tracing recent minor merging events. The rest-frame ultraviolet (UV) continuum emission often has a distribution completely different from H$\alpha$, which warns about the use of UV-SED based star formation tracers in these systems. Our analysis of galaxy dynamics shows that minor dynamical disruptions (e.g. minor merging) are generally not enough to cause a deviation from the established 'Main Sequence' relation. Most galaxies are found to follow the fundamental metallicity relation (FMR), although with large scatter. One galaxy, (a small satellite galaxy of a massive companion) is found to deviate strongly from the FMR. This deviation is in nice agreement with the correlation recently discovered in local galaxies between gas metallicity and environment, which has been ascribed to enriched inter-galactic medium (IGM) in dense environments, and therefore suggests that here the IGM was already significantly enriched by z~1.5.

The ultraviolet properties of star-forming galaxies - I. HST WFC3 observations of very high redshift galaxies

The acquisition of deep Near-IR imaging with Wide Field Camera 3 on the Hubble Space Telescope has provided the opportunity to study the very-high redshift Universe. For galaxies up to $z\approx 7.7$ sufficient wavelength coverage exists to probe the rest-frame ultraviolet (UV) continuum without contamination from either Lyman-$\alpha$ emission or the Lyman-$\alpha$ break. In this work we use Near-IR imaging to measure the rest-frame UV continuum colours of galaxies at $4.7<z<7.7$. We are have carefully defined a colour-colour selection to minimise any inherent bias in the measured UV continuum slope for the drop-out samples. For the highest-redshift sample ($6.7<z<7.7$), selected as $z_{f850lp}$-band dropouts, we find mean UV continuum colours approximately equal to zero (AB), consistent with a dust-free, solar metallicity, star forming population (or a moderately dusty population of low metallicity). At lower-redshift we find that the mean UV continuum colours of galaxies (over the same luminosity range) are redder, and that galaxies with higher luminosities are also slightly redder on average. One interpretation of this is that lower-redshift and more luminous galaxies are dustier, however this interpretation is complicated by the effects of the star formation history and metallicity and potentially the initial mass function on the UV continuum colours.

HUBBLE SPACE TELESCOPEIMAGING OF Lyα EMISSION ATz≈ 4.4

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.

New star-forming galaxies at z≈ 7 from Wide Field Camera Three imaging

The addition of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) has led to a dramatic increase in our ability to study the z>6 Universe. The increase in the near-infrared (NIR) sensitivity of WFC3 over previous instruments has enabled us to reach apparent magnitudes approaching 29 (AB). This allows us to probe the rest-frame ultraviolet (UV) continuum, redshifted into the NIR at $z>6$. Taking advantage of the large optical depths at this redshift, resulting in the Lyman-alpha break, we use a combination of WFC3 imaging and pre-existing Advanced Camera for Surveys (ACS) imaging to search for z approx 7 over 4 fields. Our analysis reveals 29 new z approx 7 star forming galaxy candidates in addition to 16 pre-existing candidates already discovered in these fields. The improved statistics from our doubling of the robust sample of z-drop candidates confirms the previously observed evolution of the bright end of the luminosity function.

DUST OBSCURATION IN LYMAN BREAK GALAXIES ATz∼ 4

Measuring star formation rates (SFRs) in high-z galaxies with their rest-frame ultraviolet (UV) continuum can be uncertain because of dust obscuration. Prior studies had used the submillimeter emission at 850 um to determine the intrinsic SFRs of rest-frame UV selected galaxies, but the results suffered from the low sensitivity and poor resolution (~15''). Here, we use ultradeep Very Large Array 1.4 GHz images with ~1''-2'' resolutions to measure the intrinsic SFRs. We perform stacking analyses in the radio images centered on ~3500 Lyman break galaxies (LBGs) at z~4 in the Great Observatories Origins Deep Survey-North and South fields selected with Hubble Space Telescope/Advanced Camera for Surveys data. The stacked radio flux is very low, 0.08+/-0.15 uJy, implying a mean SFR of 6+/-11 M/yr. This is comparable to the uncorrected mean UV SFRs of 5 M/yr, implying that the z~4 LBGs have little dust extinction. The low SFR and dust extinction support the previous results that z~4 LBGs are in general not submillimeter galaxies. We further show that there is no statistically significant excess of dust-hidden star-forming components within ~22 kpc from the LBGs.

SIZES OF LYα-EMITTING GALAXIES AND THEIR REST-FRAME ULTRAVIOLET COMPONENTS ATz= 3.1

We present a rest-frame ultraviolet analysis of ~120 z~3.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). Using Hubble Space Telescope (HST) images taken as part of the Galaxy Evolution From Morphology and SEDS (GEMS) survey, Great Observatories Origins Deep Survey (GOODS), and Hubble Ultradeep Field (HUDF) surveys, we analyze the sizes of LAEs, as well as the spatial distribution of their components, which are defined as distinct clumps of UV-continuum emission. We set an upper limit of ~1 kpc (~0.1") on the rms offset between the centroids of the continuum and Lyman-alpha emission. The star formation rates of LAE components inferred from the rest-frame ultraviolet continuum range from ~0.1 M_{sun}/yr to ~5$ M_{sun}/yr. A subsample of LAEs with coverage in multiple surveys (at different imaging depths) suggests that one needs a signal-to-noise ratio, S/N>~30, in order to make a robust estimate of the half-light radius of an LAE system. The majority of LAEs have observed half-light radii <~2 kpc, and LAE components typically have observed half-light radii <~1.5 kpc (<~ 0.2"). Although only ~50% of the detected LAE components are resolved at GOODS depth, the brightest (V<~26.3) are all resolved in both GOODS and GEMS. Since we find little evidence for a correlation between the rest-UV sizes and magnitudes of LAEs, the majority should be resolved in a deeper survey at the ~0.05" angular resolution of HST. Most of the multi-component LAEs identified in shallow frames become connected in deeper images, suggesting that the majority of the rest-UV "clumps" are individual star-forming regions within a single system.

The Space Density and Colors of Massive Galaxies at 2 &lt; z &lt; 3: The Predominance of Distant Red Galaxies

Using the deep multiwavelength MUSYC, GOODS, and FIRES surveys we construct a stellar mass-limited sample of galaxies at 2 1011 M☉ distributed over four independent fields with a total area of almost 400 arcmin2. The mean number density of massive galaxies in this redshift range ρ(M > 1011 M☉) = (2.2 ± 0.6) × 10-4 h Mpc-3. We present values and 25th and 75th percentiles for the distributions of observed RAB magnitudes, observed J - Ks colors, and rest-frame ultraviolet continuum slopes, M/LV ratios, and U - V colors. The galaxies show a large range in all these properties. The median galaxy is faint in the observer's optical (RAB = 25.9), red in the observed near-IR (J - Ks = 2.48), has a rest-frame UV spectrum that is relatively flat in Fλ (β = -0.4), and rest-frame optical colors resembling those of nearby spiral galaxies (U - V = 0.62). We determine which galaxies would be selected as Lyman break galaxies (LBGs) or distant red galaxies (DRGs, having J - Ks > 2.3) in this mass-limited sample. By number DRGs make up 69% of the sample, and LBGs 20%, with a small amount of overlap. By mass DRGs make up 77%, and LBGs 17%. Neither technique provides a representative sample of massive galaxies at 2 < z < 3 as they only sample the extremes of the population. As we show here, multiwavelength surveys with high-quality photometry are essential for an unbiased census of massive galaxies in the early universe. The main uncertainty in this analysis is our reliance on photometric redshifts; confirmation of the results presented here requires extensive near-infrared spectroscopy of optically faint samples.

Investigating the nature of the $\mathsf {\vec z}\simeq\mathsf {2.8}$ submillimeter selected galaxy SMM J02399-0136 with VLT spectropolarimetry

We present deep optical spectropolarimety of SMM J02399-0136 (z=2.8) done with the VLT Antu 8.2 m telescope equipped with FORS1. Moderate continuum and emission line polarization are measured (P~5%). We do not detect broad lines in scattered flux as would be expected for a type-2 object but rather a polarization behaviour similar to BAL quasars. This classification is confirmed by the detection of both high and low ionization broad absorption troughs and a very red continuum. We argue that this object shares several properties with local ULIGs such as Mrk 231 and other ultraluminous infrared Lo-BAL quasars. However, the fact that the ultraviolet spectrum is dominated by non-stellar radiation does not prove that the dust that is thermally radiating in the far infrared is predominantly heated by the AGN. Since the energy that we get in the far-infrared is precisely that which is removed from the ultraviolet spectrum, this could mean that the starburst is more dust-enshrouded than the AGN due to a peculiar dust distribution. The limits we place on the putative starburst contribution to the restframe ultraviolet continuum together with constraints on the amount of extinction provides an upper limit to the star formation rate of about 2000 Msun/yr, consistent with previously claimed high star formation rate in this object.

Radio galaxies at $z\sim$ 2.5: Results from Keck spectropolarimetry

In classifying the ensemble of powerful extragalactic radio sources, considerable evidence has accumulated that radio galaxies and quasars are orientation-dependent manifestations of the same parent population: massive spheroidal galaxies containing correspondingly massive black holes. One of the key factors in establishing this unification has been the signature of a hidden quasar detected in some radio galaxies in polarized light. The obscuration of our direct view of the active nucleus usually, but not necessarily exclusively, by a thick nuclear disk or torus can act conveniently as a natural coronograph that allows a much clearer view of the host of a radio galaxy than of a quasar. In this study, we exploit the opportunity to eliminate the quasar glare by performing sensitive spectropolarimetry with the Keck II telescope of a sample of radio galaxies with redshifts around 2.5. This represents the epoch when quasars were many times more common that they are now and is likely to be the period during which their host galaxies were being assembled into what become the most massive galaxies in the Universe today. We show that dust-reflected quasar light generally dominates the restframe ultraviolet continuum of these sources and that a highly clumped scattering medium results in almost grey scattering of the active galactic nucleus photons. The observations, however, do not exclude a substantial star formation rate averaged over a Gyr of evolution. The sub-mm reradiation from the scattering dust is likely to represent only a small fraction (∼10% ) of the total far infrared luminosity. An analysis of the emission lines excited in the interstellar medium of the host galaxy by the hard quasar radiation field reveals evidence of a dramatic chemical evolution within the spheroid during this epoch. Secondary nitrogen production in intermediate mass stars produces a characteristic signature in the Nv/Civ and Nv/Heii line ratios which has been seen previously in the broad line region of quasars at similar redshifts. We find intriguing correlations between the strengths of the Lyα and N v emission lines and the degree of ultraviolet continuum polarization which may represent the dispersal of dust associated with the chemical enrichment of the spheroid.

Ultra--Steep-Spectrum Radio Sources. II. Radio, Infrared, Optical, and HST Imaging of High-Redshift 4C Objects

view Abstract Citations (69) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultra--Steep-Spectrum Radio Sources. II. Radio, Infrared, Optical, and HST Imaging of High-Redshift 4C Objects Chambers, K. C. ; Miley, G. K. ; van Breugel, W. J. M. ; Bremer, M. A. R. ; Huang, J. -S. ; Trentham, N. A. Abstract We present radio, infrared, optical, and HST imaging data on eight high-redshift (z > 2) ultra-steep-spectrum 4C radio sources. The radio polarization morphologies are highly asymmetric, indicating large rotation measures across the objects. The optical morphologies are all aligned with the radio axis. The multicolor images show strong asymmetric gradients in the color of the continuum along the radio axes. No optical emission is detected from the radio lobes. Narrowband images of the redshifted Lyα emission show that the emission-line morphology is generally aligned with the radio source but does not necessarily correspond to the apparent morphology of the rest-frame ultraviolet continuum. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192338 Bibcode: 1996ApJS..106..247C Keywords: GALAXIES: ACTIVE; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: JETS; GALAXY: EVOLUTION; INFRARED: GALAXIES; POLARIZATION; RADIO CONTINUUM: GALAXIES full text sources ADS | data products SIMBAD (64) NED (9) MAST (1) ESA (1) Related Materials (1) Part 1: 1996ApJS..106..215C