Unobscured Star Formation Rate Research Articles

GA-NIFS: The core of an extremely massive protocluster at the epoch of reionisation probed with JWST/NIRSpec

The SPT0311-58 system resides in a massive dark-matter halo at z sim 6.9. It hosts two dusty galaxies (E and W) with a combined star formation rate (SFR) of sim 3500 mostly obscured and identified by the rest-frame IR emission. The surrounding field exhibits an overdensity of submillimetre sources, making it a candidate protocluster. Our main goal is to characterise the environment and the properties of the interstellar medium (ISM) within this unique system. We used spatially resolved low-resolution ($R$=100) and high-resolution ($R$=2700) spectroscopy provided by the JWST/NIRSpec Integral Field Unit to probe a field of sim 17 times 17 kpc$^2$ around this object, with a spatial resolution of sim 0.5 kpc. These observations reveal ten new galaxies at zsim 6.9 characterised by dynamical masses spanning from sim 109 to 1010 and a range in radial velocity of sim 1500 in addition to the already known E and W galaxies. The implied large number density (phi sim $) and the wide spread in velocities confirm that is at the core of a protocluster immersed in a very massive dark-matter halo of sim (5 pm 3) times 1012 and therefore represents the most massive protocluster ever found at the epoch of reionisation (EoR). We also studied the dynamical stage of its core and find that it is likely not fully virialised. The galaxies in the system exhibit a wide range of properties and evolutionary stages. The contribution of the ongoing Halpha -based unobscured SFR to the total star formation (SF) varies significantly across the galaxies in the system. Their ionisation conditions range from those typical of the field galaxies at similar redshift recently studied with JWST to those found in more evolved objects at lower redshift, with OIII varying from sim 0.25 to 1. The metallicity spans more than 0.8 dex across the FoV, reaching nearly solar values in some cases. The detailed spatially resolved spectroscopy of the E galaxy reveals that it is actively assembling its stellar mass, showing inhomogeneities in the ISM properties at subkiloparsec scales, and a metallicity gradient (sim 0.1 dex/kpc) that can be explained by accretion of low metallicity gas from the intergalactic medium. The kinematic maps also depict an unsettled disc characterised by deviations from regular rotation, elevated turbulence, and indications of a possible precollision minor merger. These JWST/NIRSpec IFS observations confirm that is at the core of an extraordinary protocluster, and reveal details of its dynamical properties. They also unveil and provide insights into the diverse properties and evolutionary stages of the galaxies residing in this unique environment.

On the dust properties of the UV galaxies in the redshift range z ∼ 0.6–1.2

ABSTRACT Far-infrared observations from the Herschel Space Observatory are used to estimate the infrared (IR) properties of ultraviolet-selected galaxies. We stack the PACS (100, 160 $\mu$m) and SPIRE (250, 350, and 500 $\mu$m) maps of the Chandra deep field south (CDFS) on a source list of galaxies selected in the rest-frame ultraviolet (UV) in a redshift range of 0.6–1.2. This source list is created using observations from the XMM–OM telescope survey in the CDFS using the UVW1 (2910 Å) filter. The stacked data are binned according to the UV luminosity function of these sources, and the average photometry of the UV-selected galaxies is estimated. By fitting modified black bodies and IR model templates to the stacked photometry, average dust temperatures and total IR luminosity are determined. The luminosity-weighted average temperatures are consistent with a weak trend of increasing temperature with redshift found by previous studies. Infrared excess, unobscured, and obscured star formation rate (SFR) values are obtained from the UV and IR luminosities. We see a trend in which dust attenuation increases as UV luminosity decreases. It remains constant as a function of IR luminosities at fixed redshift across the luminosity range of our sources. In comparison to local luminous infrared galaxies with similar SFRs, the higher redshift star-forming galaxies in the sample show a lesser degree of dust attenuation. Finally, the inferred dust attenuation is used to correct the unobscured SFR density in the redshift range 0.6–1.2. The dust-corrected SFR density is consistent with measurements from IR-selected samples at similar redshifts.

The ALMA-ALPINE [CII] survey: Kennicutt-Schmidt relation in four massive main-sequence galaxies at z ∼ 4.5

Aims. The Kennicutt-Schmidt (KS) relation between the gas and the star formation rate (SFR) surface density (Σgas − ΣSFR) is essential to understand star formation processes in galaxies. To date, it has been measured up to z ∼ 2.5 in main-sequence galaxies. In this Letter our aim is to put constraints at z ∼ 4.5 using a sample of four massive main-sequence galaxies observed by ALMA at high resolution. Methods. We obtained ∼0.3″-resolution [CII] and continuum maps of our objects, which we then converted into gas and obscured SFR surface density maps. In addition, we produced unobscured SFR surface density maps by convolving Hubble ancillary data in the rest-frame UV. We then derived the average ΣSFR in various Σgas bins, and estimated the uncertainties using a Monte Carlo sampling. Results. Our galaxy sample follows the KS relation measured in main-sequence galaxies at lower redshift, and is slightly lower than the predictions from simulations. Our data points probe the high end both in terms of Σgas and ΣSFR, and gas depletion timescales (285–843 Myr) remain similar to z ∼ 2 objects. However, three of our objects are clearly morphologically disturbed, and we could have expected shorter gas depletion timescales (≲100 Myr) similar to merger-driven starbursts at lower redshifts. This suggests that the mechanisms triggering starbursts at high redshift may be different than in the low- and intermediate-z Universe.

The ALMA REBELS Survey: discovery of a massive, highly star-forming, and morphologically complex ULIRG at z = 7.31

ABSTRACT We present Atacama Large Millimeter/Submillimeter Array (ALMA) [C ii] and ∼158 $\rm \mu m$ continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; LIR = $1.5^{+0.8}_{-0.5} \times 10^{12}$ L⊙) at z = 7.31, spectroscopically confirmed by the Reionization Era Bright Emission Line Survey (REBELS) ALMA Large Programme. REBELS-25 has a significant stellar mass of $M_{*} = \mbox{$ 8^{+4}_{-2} \times 10^{9} $}{} ~\mbox{M$_\odot $}{}$. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR $= \mbox{$199^{+101}_{-63}$}{} ~ \mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$. This is about four times the SFR estimated from an extrapolated main sequence. We also infer a [C ii]-based molecular gas mass of $M_{{\rm H}_{2}} = \mbox{$5.1^{+5.1}_{-2.6} \times 10^{10}$}{} ~\mbox{M$_\odot $}{}$, implying a molecular gas depletion time of $t_{\rm depl, {\rm H}_{2}} = \mbox{$0.3^{+0.3}_{-0.2} $}{}$ Gyr. We observe a [C ii] velocity gradient consistent with disc rotation, but given the current resolution we cannot rule out a more complex velocity structure such as a merger. The spectrum exhibits excess [C ii] emission at large positive velocities (∼500 km s−1), which we interpret as either a merging companion or an outflow. In the outflow scenario, we derive a lower limit of the mass outflow rate of 200 $\mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$, which is consistent with expectations for a star-formation-driven outflow. Given its large stellar mass, SFR, and molecular gas reservoir ∼700 Myr after the big bang, we explore the future evolution of REBELS-25. Considering a simple, conservative model assuming an exponentially declining star formation history, constant star formation efficiency, and no additional gas inflow, we find that REBELS-25 has the potential to evolve into a galaxy consistent with the properties of high-mass quiescent galaxies recently observed at z ∼ 4.

SPT-CL J2215−3537: A Massive Starburst at the Center of the Most Distant Relaxed Galaxy Cluster

We present the discovery of the most distant, dynamically relaxed cool core cluster, SPT-CL J2215−3537 (SPT2215), and its central brightest cluster galaxy (BCG) at z = 1.16. Using new X-ray observations, we demonstrate that SPT2215 harbors a strong cool core with a central cooling time of 200 Myr (at 10 kpc) and a maximal intracluster medium cooling rate of 1900 ± 400 M ⊙ yr−1. This prodigious cooling may be responsible for fueling the extended, star-forming filaments observed in Hubble Space Telescope imaging. Based on new spectrophotometric data, we detect bright [O ii] emission in the BCG, implying an unobscured star formation rate (SFR) of M ⊙ yr−1. The detection of a weak radio source (2.0 ± 0.8 mJy at 0.8 GHz) suggests ongoing feedback from an active galactic nucleus (AGN), though the implied jet power is less than half the cooling luminosity of the hot gas, consistent with cooling overpowering heating. The extreme cooling and SFR of SPT2215 are rare among known cool core clusters, and it is even more remarkable that we observe these at such high redshift, when most clusters are still dynamically disturbed. The high mass of this cluster, coupled with the fact that it is dynamically relaxed with a highly isolated BCG, suggests that it is an exceptionally rare system that must have formed very rapidly in the early universe. Combined with the high SFR, SPT2215 may be a high-z analog of the Phoenix cluster, potentially providing insight into the limits of AGN feedback and star formation in the most massive galaxies.

A Massive, Dusty, Hi Absorption–Selected Galaxy at z ≈ 2.46 Identified in a CO Emission Survey

We report a NOrthern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter/submillimeter Array search for redshifted CO emission from the galaxies associated with seven high-metallicity ([M/H] ≥ −1.03) damped Lyα absorbers (DLAs) at z ≈ 1.64–2.51. Our observations yielded one new detection of CO(3–2) emission from a galaxy at z = 2.4604 using NOEMA, associated with the z = 2.4628 DLA toward QSO B0201+365. Including previous searches, our search results in detection rates of CO emission of % and %, respectively, in the fields of DLAs with [M/H] > −0.3 and [M/H] < −0.3. Further, the Hi–selected galaxies associated with five DLAs with [M/H] > −0.3 all have high molecular gas masses, ≳5 × 1010 M ⊙. This indicates that the highest-metallicity DLAs at z ≈ 2 are associated with the most massive galaxies. The newly identified z ≈ 2.4604 Hi–selected galaxy, DLA0201+365g, has an impact parameter of ≈7 kpc to the QSO sightline, and an implied molecular gas mass of (5.04 ± 0.78) × 1010 × (α CO/4.36) × (r 31/0.55) M ⊙. Archival Hubble Space Telescope Wide Field and Planetary Camera 2 imaging covering the rest-frame near-ultraviolet (NUV) and far-ultraviolet (FUV) emission from this galaxy yield nondetections of rest-frame NUV and FUV emission, and a 5σ upper limit of 2.3 M ⊙ yr−1 on the unobscured star formation rate (SFR). The low NUV-based SFR estimate, despite the very high molecular gas mass, indicates that DLA0201+365g either is a very dusty galaxy, or has a molecular gas depletion time that is around 2 orders of magnitude larger than that of star-forming galaxies at similar redshifts.

New-generation dust emission templates for star-forming galaxies

Context. The infrared (IR) emission of dust heated by stars provides critical information for galaxy evolution studies. Unfortunately, observations are often limited to the mid-IR, making templates a necessity. Previously published templates were based on small samples of luminous galaxies, which are not necessarily representative of normal star-forming galaxies. Aims. We constructed new-generation dust templates, including instrument-specific relations and software tools that facilitate the estimation of the total IR (TIR) luminosity as well as obscured and unobscured star formation rate (SFR) based on one or several fluxes up to z = 4. For the first time, the templates include a dependence on both TIR luminosity and the specific SFR (sSFR), thereby increasing their reliability and utility for a wide range of galaxies. We also provide formulae for calculating TIR luminosities and SFR from JWST F2100W observations at 0 &lt; z ≲ 2. Methods. Our templates are based on 2584 normal star-forming galaxies spanning a wide range of stellar mass and sSFR, including sSFRs typical at higher redshifts. IR spectra and properties were obtained using CIGALE and the physically motivated Draine &amp; Li (2007, ApJ, 657, 810) dust models. The photometry from the GALEX-SDSS-WISE Legacy Catalog was supplemented with 2MASS and Herschel-ATLAS, up to 19 bands from FUV to 500 μm. Results. The shape of the dust spectrum varies with TIR luminosity, but also independently with sSFR. Remarkably precise estimates of the dust luminosity are possible with a single band over the rest-frame 12−17 μm and 55−130 μm. We validate single-band estimates on diverse populations, including local luminous IR galaxies, and find no significant systematic errors. Using two or more bands simultaneously yields the unbiased estimation of the TIR luminosity, even of star-forming dwarfs. Conclusions. We obtain fresh insights regarding the interplay between monochromatic IR luminosities, spectral shapes, and physical properties, and we constructed new templates and estimators of the dust luminosity and SFR. We provide software for generating templates and estimating these quantities based on 1−4 bands from WISE, JWST, Spitzer, and Herschel, up to z = 4.

New Radio Constraints on the Obscured Star Formation Rates of Massive GRB Hosts at Redshifts 2–3.5

Abstract It is not clear whether gamma-ray bursts (GRBs) are unbiased tracers of cosmic star formation at z &gt; 2. Since dusty starburst galaxies are significant contributors to the cosmic star formation at these redshifts, they should form a major part of the GRB host population. However, recent studies at z ≤ 2 have shown that the majority of the star formation activity in GRB hosts is not obscured by dust. Here, we investigate the galaxy-scale dust obscuration in z ∼ 2–3.5 GRB hosts preselected to have high-resolution, high signal-to-noise afterglow spectra in the rest-frame ultraviolet (UV) and thus relatively low line-of-sight dust obscuration. We present new deep Very Large Array observations of four GRB hosts, and compare the radio-based (upper limits on the) total star formation rates (SFRs) to the unobscured SFRs derived from fits to the optical-UV spectral energy distribution. The fraction of the total SFR that is obscured by dust in these galaxies is found to be &lt;90% in general, and ≲50% for GRB 021004 in particular. These observations suggest that z ∼ 2–3.5 GRBs with UV-unobscured sightlines originate in star-forming galaxies with low overall dust obscuration, unlike the dusty starburst population.

Spectral Energy Distributions of Companion Galaxies to z ∼ 6 Quasars

Abstract Massive, quiescent galaxies are already observed at redshift z ∼ 4, i.e., ∼1.5 Gyr after the big bang. Current models predict them to be formed via massive, gas-rich mergers at z &gt; 6. Recent ALMA observations of the cool gas and dust in z ≳ 6 quasars have discovered [C ii]- and far-infrared-bright galaxies adjacent to several quasars. In this work, we present sensitive imaging and spectroscopic follow-up observations, with HST/WFC3, Spitzer/IRAC, VLT/MUSE, Magellan/FIRE, and LBT/LUCI-MODS, of ALMA-detected, dust-rich companion galaxies of four quasars at z ≳ 6, specifically acquired to probe their stellar content and unobscured star formation rate. Three companion galaxies do not show significant emission in the observed optical/IR wavelength range. The photometric limits suggest that these galaxies are highly dust-enshrouded, with unobscured star formation rates SFRUV &lt; few M ⊙ yr−1, and a stellar content of M * &lt; 1010 M ⊙ yr−1. However, the companion to PJ167−13 shows bright rest-frame UV emission (F140W AB = 25.48). Its spectral energy distribution resembles that of a star-forming galaxy with a total SFR ∼ 50 M ⊙ yr−1 and M * ∼ 9 × 109 M ⊙. All the companion sources are consistent with residing on the galaxy main sequence at z ∼ 6. Additional, deeper data from future facilities, such as the James Webb Space Telescope, are needed in order to characterize these gas-rich sources in the first gigayear of cosmic history.

Gemini IFU, VLA, and HST observations of the OH Megamaser Galaxy IRAS17526 + 3253★

AbstractWe present a multiwavelength study of the OH megamaser galaxy IRAS17526 + 3253, based on new Gemini multi-object spectrograph integral field unit (GMOS/IFU) observations, Hubble Space Telescope F814W, and H α + [N ii] images, and archival 2MASS and 1.49 GHz VLA data. The Hubble Space Telescope(HST) images clearly reveal a mid-to-advanced stage major merger whose northwestern and southeastern nuclei have a projected separation of ∼8.5 kpc. Our HST/H α + [N ii] image shows regions of ongoing star formation across the envelope on ∼10 kpc scales, which are aligned with radio features, supporting the interpretation that the radio emission originates from star-forming regions. The measured H α luminosities imply that the unobscured star formation rate (SFR) is ∼10–30 M⊙ yr−1. The GMOS/IFU data reveal two structures in northwestern separated by 850 pc and by a discontinuity in the velocity field of ∼ 200 km s−1. We associate the blueshifted and redshifted components with, respectively, the distorted disc of northwestern and tidal debris, possibly a tail originating in southeastern. Star formation is the main ionization source in both components, which have SFRs of ∼2.6–7.9 M⊙ yr−1 and ∼1.5–4.5 M⊙ yr−1, respectively. Fainter line emission bordering these main components is consistent with shock ionization at a velocity ∼200 km s−1 and may be the result of an interaction between the tidal tail and the northwestern galaxy’s disc. IRAS17526 + 3253 is one of only a few systems known to host both luminous OH and H2O masers. The velocities of the OH and H2O maser lines suggest that they are associated with the northwestern and southeastern galaxies, respectively (Martin et al.; Wagner).

Star formation history from the cosmic infrared background anisotropies

We present a linear clustering model of cosmic infrared background (CIB) anisotropies at large scales that is used to measure the cosmic star formation rate density up to redshift 6, the effective bias of the CIB, and the mass of dark matter halos hosting dusty star-forming galaxies. This is achieved using the Planck CIB auto- and cross-power spectra (between different frequencies) and CIB × CMB (cosmic microwave background) lensing cross-spectra measurements, as well as external constraints (e.g. on the CIB mean brightness). We recovered an obscured star formation history which agrees well with the values derived from infrared deep surveys and we confirm that the obscured star formation dominates the unobscured formation up to at least z = 4. The obscured and unobscured star formation rate densities are compatible at 1σ at z = 5. We also determined the evolution of the effective bias of the galaxies emitting the CIB and found a rapid increase from ~0.8 at z = 0 to ~8 at z = 4. At 2 &lt; z &lt; 4, this effective bias is similar to that of galaxies at the knee of the mass functions and submillimetre galaxies. This effective bias is the weighted average of the true bias with the corresponding emissivity of the galaxies. The halo mass corresponding to this bias is thus not exactly the mass contributing the most to the star formation density. Correcting for this, we obtained a value of log(Mh/M⊙) = 12.77−0.125+0.128 for the mass of the typical dark matter halo contributing to the CIB at z = 2. Finally, using a Fisher matrix analysis we also computed how the uncertainties on the cosmological parameters affect the recovered CIB model parameters, and find that the effect is negligible.

Revealing the Host Galaxy of a Quasar 2175 Å Dust Absorber at z = 2.12

Abstract We report the first detection of the host galaxy of a strong 2175 Å dust absorber at z = 2.12 toward the background quasar SDSS J121143.42+083349.7 using Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) IR F140W direct imaging and G141 grism spectroscopy. The spectroscopically confirmed host galaxy is located at a small impact parameter of ∼5.5 kpc (∼0.″65). The F140W image reveals a disk-like morphology with an effective radius of 2.24 ± 0.08 kpc. The extracted 1D spectrum is dominated by a continuum with weak emission lines ([O iii] and [O ii]). The [O iii]-based unobscured star formation rate (SFR) is 9.4 ± 2.6 M ⊙ yr−1, assuming an [O iii]/Hα ratio of 1. The moderate 4000 Å break (Dn(4000) index ∼1.3) and Balmer absorption lines indicate that the host galaxy contains an evolved stellar population with an estimated stellar mass M * of (3–7) × 1010 M ⊙. The SFR and M * of the host galaxy are comparable to, though slightly lower than, those of typical emission-selected galaxies at z ∼ 2. As inferred from our absorption analysis in Ma et al., the host galaxy is confirmed to be a chemically enriched, evolved, massive, and star-forming disk-like galaxy that is likely in the transition from a blue star-forming galaxy to a red quiescent galaxy.

A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21

Abstract Interactions between pairs of isolated dwarf galaxies provide a critical window into low-mass hierarchical, gas-dominated galaxy assembly and the build-up of stellar mass in low-metallicity systems. We present the first Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) optical integral field unit (IFU) observations of the interacting dwarf pair dm1647+21 selected from the TiNy Titans survey. The Hα emission is widespread and corresponds to a total unobscured star formation rate (SFR) of 0.44 M ⊙ yr−1, which is 2.7 times higher than the SFR inferred from Sloan Digital Sky Survey (SDSS) data. The implied specific SFR (sSFR) for the system is elevated by more than an order of magnitude above non-interacting dwarfs in the same mass range. This increase is dominated by the lower-mass galaxy, which has a sSFR enhancement of &gt;50. Examining the spatially resolved maps of classic optical line diagnostics, we find that the interstellar medium (ISM) excitation can be fully explained by star formation. The velocity field of the ionized gas is not consistent with simple rotation. Dynamical simulations indicate that the irregular velocity field and the stellar structure is consistent with the identification of this system as an ongoing interaction between two dwarf galaxies. The widespread, clumpy enhancements in the star formation in this system point to important differences in the effect of mergers on dwarf galaxies, compared to massive galaxies; rather than the funneling of gas to the nucleus and giving rise to a nuclear starburst, starbursts in low-mass galaxy mergers may be triggered by large-scale ISM compression, and thus may be more distributed.

Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z &gt; 4 Lensed by a Frontier Fields Cluster

Abstract We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z &gt; 4 and the strong lensing model (μ = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 1010 L ⊙ and an obscured star formation rate of 14.6 ± 4.5 M ⊙ yr−1. The unobscured star formation rate from the UV is only 4.1 ± 0.3 M ⊙ yr−1, which means the total star formation rate (18.7 ± 4.5 M ⊙ yr−1) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 109 M ⊙, MACS0717_Az9 is one of only a handful of z &gt; 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe.

Kband SINFONI spectra of twoz~ 5 submillimeter galaxy systems: upper limits to the unobscured star formation from [O II] optical emission line searches

We present deep SINFONI K band integral field spectra of two submillimeter (SMG) galaxy systems: BR 1202-0725 and J1000+0234, at $z=4.69$ and $4.55$ respectively. Spectra extracted for each object in the two systems do not show any signature of the [O II]$\lambda\lambda$3726,29\AA$\,$ emission-lines, placing upper flux limits of $3.9$ and $2.5 \times 10^{-18}\,$${\rm erg\,s^{-1}\,\,cm^{-2} \,}$ for BR 1202-0725 and J1000+0234, respectively. Using the relation between the star formation rate (SFR) and the luminosity of the [O II] doublet from Kennicutt (1998), we estimate unobscured SFR upper limits of $\sim$ $10-15\,\rm M_\odot\,yr^{-1} \,$ and $\sim$ $30-40\,\rm M_\odot\,yr^{-1} \,$ for the objects of the two systems, respectively. For the SMGs, these values are at least two orders of magnitude lower than those derived from SED and IR luminosities. The differences on the SFR values would correspond to internal extinction of, at least, $3.4 - 4.9$ and $2.1 - 3.6$ mag in the visual for BR 1202-0725 and J1000+0234 SMGs, respectively. The upper limit for the [O II]-derived SFR in one of the LAEs (Ly$\alpha2$) in the BR1202-0725 system is at least one order of magnitude lower than the previous SFR derived from infrared tracers, while both estimates are in good agreement for Ly$\alpha$1. The lower limits to the internal extinction in these two Lyman-alpha emitters (LAEs) are $0.6$ mag and $1.3$ mag, respectively. No evidence for the previously claimed (Ohta et al. 2000) [O II] emission associated with Ly$\alpha$1 is identified in our data, implying that residuals of the K-band sky emission lines after subtraction in medium-band imaging data could provide the adequate flux.

Star formation and black hole accretion activity in rich local clusters of galaxies

We present a study of the star formation and central black hole accretion activity of the galaxies hosted in the two nearby (z$\sim$0.2) rich galaxy clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations ($\sim$ 3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star forming members of the two clusters present star formation rates comparable with those measured in coeval field galaxies. The analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions: The analysis of the specific star formation rate reveals evidence of on-going galaxy pre-processing along A1731's filament-like structure. Furthermore, the decrease in the number of star forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity.

HOT DUST OBSCURED GALAXIES WITH EXCESS BLUE LIGHT: DUAL AGN OR SINGLE AGN UNDER EXTREME CONDITIONS?

ABSTRACT Hot dust-obscured galaxies (Hot DOGs) are a population of hyper-luminous infrared galaxies identified by the Wide-field Infrared Survey Explorer (WISE) mission from their very red mid-IR colors, and characterized by hot dust temperatures (T &gt; 60 K). Several studies have shown clear evidence that the IR emission in these objects is powered by a highly dust-obscured active galactic nucleus (AGN) that shows close to Compton-thick absorption at X-ray wavelengths. Thanks to the high AGN obscuration, the host galaxy is easily observable, and has UV/optical colors usually consistent with those of a normal galaxy. Here we discuss a sub-population of eight Hot DOGs that show enhanced rest-frame UV/optical emission. We discuss three scenarios that might explain the excess UV emission: (i) unobscured light leaked from the AGN by reflection over the dust or by partial coverage of the accretion disk; (ii) a second unobscured AGN in the system; or (iii) a luminous young starburst. X-ray observations can help discriminate between these scenarios. We study in detail the blue excess Hot DOG WISE J020446.13–050640.8, which was serendipitously observed by Chandra/ACIS-I for 174.5 ks. The X-ray spectrum is consistent with a single, hyper-luminous, highly absorbed AGN, and is strongly inconsistent with the presence of a secondary unobscured AGN. Based on this, we argue that the excess blue emission in this object is most likely either due to reflection or a co-eval starburst. We favor the reflection scenario as the unobscured star formation rate needed to power the UV/optical emission would be ≳1000 M ⊙ yr−1. Deep polarimetry observations could confirm the reflection hypothesis.

Are quiescent galaxies truly devoid of star formation? The mid-, far-infrared and radio properties of quiescent galaxies at z = 0.1 - 3

AbstractQuiescent galaxy candidates are typically identified by their low unobscured star formation rates from deep field photometric surveys. However, their selection technique relies on the assumption of a universal dust attenuation curve. It is important to verify the selection through independent SFR indicators at longer wavelengths. Current mid-, far-infrared and radio surveys are limited to detecting only galaxies with very strong star formation or AGN activity. Here, I present the first comprehensive stacking results across mid-, far-infrared and radio wavelengths using Spitzer, Herschel and VLA data in the COSMOS field (Man et al. 2014). We find that the rest-frame NUV-r and r-J color criteria, combined with low 24 μm emission, provides a robust selection of truly quiescent galaxies out to z = 3. Additionally, we find evidence of radio emission in excess of the expected total star formation in quiescent galaxies at z ~ 0-1.5, indicative of a ubiquitous presence of low-luminosity radio AGN among them.

ULTRAVIOLET MORPHOLOGY AND UNOBSCURED UV STAR FORMATION RATES OF CLASH BRIGHTEST CLUSTER GALAXIES

Brightest cluster galaxies (BCGs) are usually quiescent, but many exhibit star formation. Here we exploit the opportunity provided by rest-frame UV imaging of galaxy clusters in the CLASH (Cluster Lensing and Supernovae with Hubble) Multi-Cycle Treasury Project to reveal the diversity of UV morphologies in BCGs and to compare them with recent simulations of the cool, star-forming gas structures produced by precipitation-driven feedback. All of the CLASH BCGs are detected in the rest-frame UV (280 nm), regardless of their star-formation activity, because evolved stellar populations produce a modest amount of UV light that traces the relatively smooth, symmetric, and centrally peaked stellar distribution seen in the near infrared. Ultraviolet morphologies among the BCGs with strong UV excesses exhibit distinctive knots, multiple elongated clumps, and extended filaments of emission that distinctly differ from the smooth profiles of the UV-quiet BCGs. These structures, which are similar to those seen in the few star-forming BCGs observed in the UV at low redshift, are suggestive of bi-polar streams of clumpy star formation, but not of spiral arms or large, kpc-scale disks. Based on the number of streams and lack of culprit companion galaxies, these streams are unlikely to have arisen from multiple collisions with gas-rich galaxies. These star-forming UV structures are morphologically similar to the cold-gas structures produced in simulations of precipitation-driven AGN feedback in which jets uplift low-entropy gas to greater altitudes, causing it to condense. Unobscured star-formation rates estimated from CLASH UV images using the Kennicutt relation range up to 80 solar masses per year in the most extended and highly structured systems. The circumgalactic gas-entropy threshold for star formation in CLASH BCGs at z~0.2-0.5 is indistinguishable from that for clusters at z < 0.2.

Directly imaging damped Ly α galaxies at z &gt; 2 – III. The star formation rates of neutral gas reservoirs at z ∼ 2.7

We present results from a survey designed to probe the star formation properties of 32 damped Ly-alpha systems (DLAs) at z~2.7. By using the "double-DLA" technique that eliminates the glare of the bright background quasars, we directly measure the rest-frame FUV flux from DLAs and their neighbouring galaxies. At the position of the absorbing gas, we place stringent constraints on the unobscured star formation rates (SFRs) of DLAs to 2-sigma limits of <0.09-0.27 M/yr, corresponding to SFR surface densities <10^(-2.6)-10^(-1.5) M/yr/kpc^2. The implications of these limits for the star formation law, metal enrichment, and cooling rates of DLAs are examined. By studying the distribution of impact parameters as a function of SFRs for all the galaxies detected around these DLAs, we place new direct constraints on the bright end of the UV luminosity function of DLA hosts. We find that <13% of the hosts have SFR>2 M/yr at impact parameters b < (SFR/(M/yr))^(0.8)+6 kpc, differently from current samples of confirmed DLA galaxies. Our observations also disfavor a scenario in which the majority of DLAs arise from bright LBGs at distances 20 < b < 100 kpc. These new findings corroborate a picture in which DLAs do not originate from highly star forming systems that are coincident with the absorbers, and instead suggest that DLAs are associated with faint, possibly isolated, star-forming galaxies. Potential shortcomings of this scenario and future strategies for further investigation are discussed.