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Register a new userIRAM 30m-EMIR Redshift Search of z = 3-4 Lensed Dusty Starbursts selected from the HerBS sample
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Using the EMIR instrument on the IRAM 30m telescope, we conducted a spectroscopic redshift search of seven z$_{rm phot}$ $sim$ 4 sub-millimetre bright galaxies selected from the Herschel Bright Sources (HerBS) sample with fluxes at 500 $mu$m greater than 80 mJy. For four sources, we obtained spectroscopic redshifts between 3.4 < z < 4.1 through the detection of multiple CO-spectral lines with J $leq$ 3. Later, we detected low-J transitions for two of these sources with the GBT including the CO(1-0) transition. For the remaining three sources, more data are needed to determine the spectroscopic redshift unambiguously. The measured CO luminosities and line widths suggest that all these sources are gravitationally lensed. These observations demonstrate that the 2 mm window is indispensable to confirm robust spectroscopic redshifts for z < 4 sources. Finally, we present an efficient graphical method to correctly identify spectroscopic redshifts.
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We present ALMA, NOEMA, and IRAM-30m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at z~3-3.5, part of the Plancks Dusty GEMS sample, to probe the gas reservoirs closely associated with their exceptional levels of star formation. We obtain robust detections of ten emission lines between J_up=4 and 6, as well as several additional flux upper limits. In PLCK_G244.8+54.9, the brightest source at z=3.0, the HNC(5-4) line emission at 0.1 resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. The HCO+/HCN > 1 and HNC/HCN ~ 1 line ratios in our sample are similar to those of nearby ULIRGs and consistent with photon-dominated regions without any indication of important mechanical heating or AGN feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with H2 density n~10^5-6 cm^-3, although important degeneracies prevent determining the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z~3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional compared to other lensed dusty star-forming galaxies at z>2 and fall near the upper envelope of local ULIRGs. Our results also favor constant dense-gas depletion times in these populations.
We present ci,(2--1) and multi-transition $^{12}$CO observations of a dusty star-forming galaxy, ACT,J2029+0120, which we spectroscopically confirm to lie at $z$,=,2.64. We detect CO(3--2), CO(5--4), CO(7--6), CO(8--7), and ci,(2--1) at high significance, tentatively detect HCO$^{+}$(4--3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4--3) and CS(7--6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy of the textit{Herschel} Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T$sim$117 K and $n_{text{H}_2}sim10^5$ cm$^{-3}$, most consistent with a ULIRG/QSO object and the presence of high density tracers. We also find that the velocity width of the ci line is potentially larger than seen in all CO transitions for this object, and that the $L_{rm C,I(2-1)}/L_{rm CO(3-2)}$ ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.
Water ($rm H_{2}O$), one of the most ubiquitous molecules in the universe, has bright millimeter-wave emission lines easily observed at high-redshift with the current generation of instruments. The low excitation transition of $rm H_{2}O$, p$-$$rm H_{2}O$(202 $-$ 111) ($ u_{rest}$ = 987.927 GHz) is known to trace the far-infrared (FIR) radiation field independent of the presence of active galactic nuclei (AGN) over many orders-of-magnitude in FIR luminosity (L$_{rm FIR}$). This indicates that this transition arises mainly due to star formation. In this paper, we present spatially ($sim$0.5 arcsec corresponding to $sim$1 kiloparsec) and spectrally resolved ($sim$100 kms$^{-1}$) observations of p$-$$rm H_{2}O$(202 $-$ 111) in a sample of four strong gravitationally lensed high-redshift galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA). In addition to increasing the sample of luminous ($ > $ $10^{12}$L$_{odot}$) galaxies observed with $rm H_{2}O$, this paper examines the L$_{rm H_{2}O}$/L$_{rm FIR}$ relation on resolved scales for the first time at high-redshift. We find that L$_{rm H_{2}O}$ is correlated with L$_{rm FIR}$ on both global and resolved kiloparsec scales within the galaxy in starbursts and AGN with average L$_{rm H_{2}O}$/L$_{rm FIR}$ =$2.76^{+2.15}_{-1.21}times10^{-5}$. We find that the scatter in the observed L$_{rm H_{2}O}$/L$_{rm FIR}$ relation does not obviously correlate with the effective temperature of the dust spectral energy distribution (SED) or the molecular gas surface density. This is a first step in developing p$-$$rm H_{2}O$(202 $-$ 111) as a resolved star formation rate (SFR) calibrator.
We exploit the continuity equation approach and the `main sequence star-formation timescales to show that the observed high abundance of galaxies with stellar masses > a few 10^10 M_sun at redshift z>4 implies the existence of a galaxy population featuring large star formation rates (SFRs) > 10^2 M_sun/yr in heavily dust-obscured conditions. These galaxies constitute the high-redshift counterparts of the dusty star-forming population already surveyed for z<3 in the far-IR band by the Herschel space observatory. We work out specific predictions for the evolution of the corresponding stellar mass and SFR functions out to z~10, elucidating that the number density at z<8 for SFRs >30 M_sun/yr cannot be estimated relying on the UV luminosity function alone, even when standard corrections for dust extinction based on the UV slope are applied. We compute the number counts and redshift distributions (including galaxy-scale gravitational lensing) of this galaxy population, and show that current data from AzTEC-LABOCA, SCUBA-2 and ALMA-SPT surveys are already digging into it. We substantiate how an observational strategy based on a color preselection in the far-IR or (sub-)mm band with Herschel and SCUBA-2, supplemented by photometric data via on-source observations with ALMA, can allow to reconstruct the bright end of the SFR functions out to z~8. In parallel, such a challenging task can be managed by exploiting current UV surveys in combination with (sub-)mm observations by ALMA and NIKA2 and/or radio observations by SKA and its precursors.
Verifying that sub-mm galaxies (SMGs) are gravitationally lensed requires time-expensive observations with over-subscribed high-resolution observatories. Here, we aim to strengthen the evidence of gravitational lensing within the Herschel Bright Sources (HerBS) by cross-comparing their positions to optical (SDSS) and near-infrared (VIKING) surveys, in order to search for the foreground lensing galaxy candidates. Resolved observations of the brightest HerBS sources have already shown that most are lensed, and a galaxy evolution model predicts that $sim$76% of the total HerBS sources are lensed, although with the SDSS survey we are only able to identify the likely foreground lenses for 25% of the sources. With the near-infrared VIKING survey, however, we are able to identify the likely foreground lenses for 57% of the sources, and we estimate that 82% of the HerBS sources have lenses on the VIKING images even if we cannot identify the lens in every case. We find that the angular offsets between lens and Herschel source are larger than that expected if the lensing is done by individual galaxies. We also find that the fraction of HerBS sources that are lensed falls with decreasing 500-micron flux density, which is expected from the galaxy evolution model. Finally, we apply our statistical VIKING cross-identification to the entire Herschel-ATLAS catalogue, where we also find that the number of lensed sources falls with decreasing 500-micron flux density.
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