Low, Milky-Way like, Molecular Gas Excitation of Massive Disk Galaxies at z~1.5

We present evidence for Milky-Way-like, low-excitation molecular gas reservoirs in near-IR selected massive galaxies at z~1.5, based on IRAM Plateau de Bure Interferometer CO[3-2] and NRAO Very Large Array CO[1-0] line observations for two galaxies that had been previously detected in CO[2-1] emission. The CO[3-2] flux of BzK-21000 at z=1.522 is comparable within the errors to its CO[2-1] flux, implying that the CO[3-2] transition is significantly sub-thermally excited. The combined CO[1-0] observations of the two sources result in a detection at the 3 sigma level that is consistent with a higher CO[1-0] luminosity than that of CO[2-1]. Contrary to what is observed in submillimeter galaxies and QSOs, in which the CO transitions are thermally excited up to J>=3, these galaxies have low-excitation molecular gas, similar to that in the Milky Way and local spirals. This is the first time that such conditions have been observed at high redshift. A Large Velocity Gradient analysis suggests that molecular clouds with density and kinetic temperature comparable to local spirals can reproduce our observations. The similarity in the CO excitation properties suggests that a high, Milky-Way-like, CO to H_2 conversion factor could be appropriate for these systems. If such low-excitation properties are representative of ordinary galaxies at high redshift, centimeter telescopes such as the Expanded Very Large Array and the longest wavelength Atacama Large Millimeter Array bands will be the best tools for studying the molecular gas content in these systems through the observations of CO emission lines.Comment: 5 pages, 4 figures. ApJ Letters in pres

Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies

We present evidence for very high gas fractions and extended molecular gas reservoirs in normal, near-infrared selected (BzK) galaxies at z~1.5, based on multi-configuration CO[2-1] observations obtained at the IRAM PdBI. Six of the six galaxies observed were securely detected. High resolution observations resolve the CO emission in four of them, implying sizes of order of 6-11 kpc and suggesting the presence of rotation. The UV morphologies are consistent with clumpy, unstable disks, and the UV sizes are consistent with the CO sizes. The star formation efficiencies are homogeneously low and similar to local spirals - the resulting gas depletion times are ~0.5 Gyr, much higher than what is seen in high-z submm galaxies and quasars. The CO luminosities can be predicted to within 0.15 dex from the star formation rates and stellar masses, implying a tight correlation of the gas mass with these quantities. We use dynamical models of clumpy disk galaxies to derive dynamical masses. These models are able to reproduce the peculiar spectral line shapes of the CO emission. After accounting for the stellar and dark matter masses we derive gas masses of 0.4-1.2x10^11 Msun. The conversion factor is very high: alpha_CO=3.6+-0.8, consistent with the Galaxy but four times higher than that of local ultra-luminous IR galaxies. The gas accounts for an impressive 50-65% of the baryons within the galaxies' half light radii. We are witnessing truly gas-dominated galaxies at z~1.5, a finding that explains the high specific SFRs observed for z>1 galaxies. The BzK galaxies can be viewed as scaled-up versions of local disk galaxies, with low efficiency star formation taking place inside extended, low excitation gas disks. They are markedly different than local ULIRGs and high-z submm galaxies, which have more excited and compact gas.Comment: Accepted for publication in Astrophysical Journal, 22 pages, 18 figures, minor revision

Near-IR bright galaxies at z~2. Entering the spheroid formation epoch ?

Spectroscopic redshifts have been measured for 9 K-band luminous galaxies at 1.7 < z < 2.3, selected with Ks < 20 in the "K20 survey" region of the Great Observatories Origins Deep Survey area. Star formation rates (SFRs) of ~100-500 Msun/yr are derived when dust extinction is taken into account. The fitting of their multi-color spectral energy distributions indicates stellar masses M ~ 10^11 Msun for most of the galaxies. Their rest-frame UV morphology is highly irregular, suggesting that merging-driven starbursts are going on in these galaxies. Morphologies tend to be more compact in the near-IR, a hint for the possible presence of older stellar populations. Such galaxies are strongly clustered, with 7 out of 9 belonging to redshift spikes, which indicates a correlation length r_0 ~ 9-17 h^-1 Mpc (1 sigma range). Current semianalytical models of galaxy formation appear to underpredict by a large factor (about 30) the number density of such a population of massive and powerful starburst galaxies at z ~ 2. The high masses and SFRs together with the strong clustering suggest that at z ~ 2 we may have started to explore the major formation epoch of massive early-type galaxies.Comment: accepted on June 17. To appear on ApJ Letter

‘Lots of Black people are on meds because they're seen as aggressive’: STOMP, COVID-19 and anti-racism in community learning disability services

Background The STOMP agenda (Stopping Over-Medication of People with learning disabilities, autism, or both) drew focus to individuals with a diagnosis of a learning disability being prescribed psychotropic medication to manage ‘behaviours that challenge’. The following study is an audit of two community learning disability services in the London boroughs of Westminster and Kensington and Chelsea for compliance with national guidance on the use of medication in this population, the impact of the COVID-19 pandemic, and equality, diversity and anti-racism. Method Routinely collected data were audited relating to clients identified in each service, totalling 54 participants. Data were audited against five standards: minimum effective dose, medication reviews, alternative multidisciplinary input, the impact of the COVID-19 pandemic and equality, diversity and anti–racism. Comparisons were made to the overall caseload (N = 365) where appropriate. Results Evidence demonstrated a greater risk of receiving psychotropic medication to manage behaviours that challenge for service users from racialised backgrounds, further evidencing institutional and/or individualised racism within practice for this population. Prescriptions also increased in dosage during the COVID-19 pandemic exacerbated by insufficient provision of alternative input and regular multi-disciplinary review as required by national guidance. Conclusions Community learning disability teams require dedicated, co-produced STOMP pathways to review those at risk of over-medication. Additional research is required to explore individual and systemic factors contributing to ethnic disparities in medication prescription for behaviours that challenge among people with learning disabilities. Further recommendations are considered around developing data collection, service user involvement, and future directions.Accessible summary: - Abuse at care home (Winterbourne View) led the NHS to start a campaign known as STOMP to make sure people with learning disabilities and/or autism got the right medication. - We looked at the medications people with learning disabilities in our area were given. We looked at how often these medications were checked by a doctor. We looked at what other support people were given. - We also looked at how people with learning disabilities were affected by COVID-19. We also looked at differences between people from different racial backgrounds. - We found that some people were given more medications to manage their behaviour. We found that the medications were not checked as often as they should be. This happened most for Black, Brown, and Asian people. - We spoke to a local service user project about our findings. They said they think racism is one of the reasons for more medications. They also said it is bad that people are on too much medication and that people should get more support

A wide area survey for high-redshift massive galaxies. I. Number counts and clustering of BzKs and EROs

We have combined deep BRIz' imaging over 2x940 arcmin^2 fields obtained with the Suprime-Cam on the Subaru telescope with JKs imaging with the SOFI camera at the New Technology Telescope to search for high-redshift massive galaxies. K-band selected galaxies have been identified over an area of ~920 arcmin^2 to K_Vega=19.2, of which 320 arcmin^2 are complete to K_Vega=20. The BzK selection technique was used to obtain complete samples of ~500 candidate massive star-forming galaxies (sBzKs) and ~160 candidate massive, passively-evolving galaxies (pBzKs), both at 1.4 5 criterion we also identified ~850 extremely red objects (EROs). The surface density of sBzKs and pBzKs is found to 1.20+/-0.05 arcmin^{-2} and 0.38+/-0.03 arcmin^{-2}, respectively. Both sBzKs and pBzKs are strongly clustered, at a level at least comparable to that of EROs, with pBzKs appearing more clustered than sBzKs. We estimate the reddening, star formation rates (SFRs) and stellar masses (M_*) of the sBzKs, confirming that to K_Vega~20 median values are M_*~10^{11}M_sun, SFR 190M_sun yr^{-1}, and E(B-V)~0.44. The most massive sBzKs are also the most actively star-forming, an effect which can be seen as a manifestation of downsizing at early epochs. The space density of massive pBzKs at z~1.4-2 is 20%+/-7% that of similarly massive early-type galaxies at z~0, and similar to that of sBzKs of the same mass. We argue that star formation quenching in these sBzKs will result in nearly doubling the space density of massive early-type galaxies, thus matching their local density.Comment: 19 pages, 13 figures, accepted by ApJ. While checking the proofs we became aware of a material mistake of non-trivial scientific relevance. In the original it was reported that the comoving volume density of passive BzK-selected galaxies with =1.7 and more massive than 10^{11}M_sun was 45%+/-15% of the local number density of similarly massive early-type galaxies. This fraction actually turns out to be 20%+/-7%. Section 6.4, point 5 in section 7, and the abstract have been modified accordingl

Expanded Very Large Arrays Observations of a Proto-Cluster of Molecular Gas-Rich Galaxies at z = 4.05

We present observations of the molecular gas in the GN20 proto-cluster of galaxies at z = 4.05 using the Expanded Very Large Array (EVLA). This group of galaxies is the ideal laboratory for studying the formation of massive galaxies via luminous, gas-rich starbursts within 1.6 Gyr of the big bang. We detect three galaxies in the proto-cluster in CO 2-1 emission, with gas masses (H_2) between 10^(10) and 10^(11) × (α/0.8) M_⊙. The emission from the brightest source, GN20, is resolved with a size ~2'' and has a clear north-south velocity gradient, possibly indicating ordered rotation. The gas mass in GN20 is comparable to the stellar mass (1.3 × 10^(11) × (α/0.8) M_⊙ and 2.3 × 10^(11) M_⊙, respectively), and the sum of gas plus stellar mass is comparable to the dynamical mass of the system (~3.4 × 10^(11)[sin (i)/sin (45°)]^(–2) M_⊙), within a 5 kpc radius. There is also evidence for a tidal tail extending another 2'' north of the galaxy with a narrow velocity dispersion. GN20 may be a massive, gas-rich disk that is gravitationally disturbed, but not completely disrupted. There is one Lyman-break galaxy (BD29079) in the GN20 proto-cluster with an optical spectroscopic redshift within our search volume, and we set a 3σ limit to the molecular gas mass of this galaxy of 1.1 × 10^(10) × (α/0.8) M_⊙

A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5

A simple two color selection based on B-, z-, and K- band photometry is proposed for culling galaxies at 1.4<z<2.5 in K-selected samples and classifying them as star-forming or passive systems. The method is calibrated on the highly complete spectroscopic redshift database of the K20 survey, verified with simulations and tested on other datasets. Requiring BzK=(z-K)-(B-z)>-0.2 (AB) allows to select actively star-forming galaxies at z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2 and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs and masses of BzK-selected galaxies are derived, and calibrated on K<20 galaxies. Based on their UV (reddening-corrected), X-ray and radio luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing the passively evolving galaxies, the UV selection appears to miss some relevant fraction of the z~2 star-forming galaxies with K<20, and hence of the (obscured) star-formation rate density at this redshift. The high SFRs and masses add to other existing evidence that these z=2 star-forming galaxies may be among the precursors of z=0 early-type galaxies. Theoretical models cannot reproduce simultaneously the space density of both passively evolving and highly star-forming galaxies at z=2. In view of Spitzer Space Telescope observations, an analogous technique based on the RJL photometry is proposed to complement the BzK selection and to identify massive galaxies at 2.5<z<4.0. These color criteria should help in completing the census of the stellar mass and of the star-formation rate density at high redshift (abridged).Comment: 19 pages, 17 figures, to appear on ApJ (20 December 2004 issue

The kiloparsec-scale star formation law at redshift 4: wide-spread, highly efficient star formation in the dust-obscured starburst galaxy GN20

We present high-resolution observations of the 880 $\mu$m (rest-frame FIR) continuum emission in the z$=$4.05 submillimeter galaxy GN20 from the IRAM Plateau de Bure Interferometer (PdBI). These data resolve the obscured star formation in this unlensed galaxy on scales of 0.3$^{\prime\prime}$$\times$0.2$^{\prime\prime}$ ($\sim$2.1$\times$1.3 kpc). The observations reveal a bright (16$\pm$1 mJy) dusty starburst centered on the cold molecular gas reservoir and showing a bar-like extension along the major axis. The striking anti-correlation with the HST/WFC3 imaging suggests that the copious dust surrounding the starburst heavily obscures the rest-frame UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no evidence for variations in the dust properties across the source within the uncertainties, consistent with extended star formation, and the peak star formation rate surface density (119$\pm$8 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$) implies that the star formation in GN20 remains sub-Eddington on scales down to 3 kpc$^2$. We find that the star formation efficiency is highest in the central regions of GN20, leading to a resolved star formation law with a power law slope of $\Sigma_{\rm SFR}$ $\sim$ $\Sigma_{\rm H_2}^{\rm 2.1\pm1.0}$, and that GN20 lies above the sequence of normal star-forming disks, implying that the dispersion in the star formation law is not due solely to morphology or choice of conversion factor. These data extend previous evidence for a fixed star formation efficiency per free-fall time to include the star-forming medium on $\sim$kpc-scales in a galaxy 12 Gyr ago.Comment: 6 pages, 5 figures, accepted to ApJ

Evidence for a clumpy, rotating gas disk in a submillimeter galaxy at z=4

We present Karl G. Jansky Very Large Array (VLA) observations of the CO(2-1) emission in the z=4.05 submillimeter galaxy (SMG) GN20. These high-resolution data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr after the Big Bang. The data reveal a clumpy, extended gas reservoir, 14 +/- 4 kpc in diameter, in unprecedented detail. A dynamical analysis shows that the data are consistent with a rotating disk of total dynamical mass 5.4 +/- 2.4 X 10^11 M_sun. We use this dynamical mass estimate to constrain the CO-to-H_2 mass conversion factor (alpha_CO), finding alpha_CO=1.1 +/- 0.6 M_sun (K km s^-1 pc^2)^-1. We identify five distinct molecular gas clumps in the disk of GN20 with masses a few percent of the total gas mass, brightness temperatures of 16-31K, and surface densities of >3,200-4,500 X (alpha_CO/0.8) M_sun pc^-2. Virial mass estimates indicate they could be self-gravitating, and we constrain their CO-to-H_2 mass conversion factor to be <0.2-0.7 M_sun (K km s^-1 pc^2)^-1. A multiwavelength comparison demonstrates that the molecular gas is concentrated in a region of the galaxy that is heavily obscured in the rest-frame UV/optical. We investigate the spatially-resolved gas excitation and find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with star formation occuring over a large portion of the disk. We discuss the implications of our results in the context of different fueling scenarios for SMGs.Comment: 15 pages, 9 figures, accepted for publication in Ap

A molecular line scan in the Hubble Deep Field North

We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z2. We reach a CO detection limit that is deep enough to detect essentially all z>1 CO lines reported in the literature so far. We have developed and applied different line searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ~2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available SEDs. Two secure CO detections in our scan are identified with star-forming galaxies at z=1.784 and at z=2.047. These galaxies have colors consistent with the `BzK' color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF850.1 at z=5.183. We consider an additional 9 line candidates as high quality. Our observations also provide a deep 3mm continuum map (1-sigma noise level = 8.6 μJy/beam). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the SFR density at 1<z<3, unless high dust temperatures are invoked. The present study represents a first, fundamental step towards an unbiased census of molecular gas in `normal' galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era