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Register a new userHerschel protocluster survey: A search for dusty star-forming galaxies in protoclusters at z=2-3
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We present a Herschel/SPIRE survey of three protoclusters at z=2-3 (2QZCluster, HS1700, SSA22). Based on the SPIRE colours (S350/S250 and S500/S350) of 250 $mu$m sources, we selected high redshift dusty star-forming galaxies potentially associated with the protoclusters. In the 2QZCluster field, we found a 4-sigma overdensity of six SPIRE sources around 4.5 (~2.2 Mpc) from a density peak of H$alpha$ emitters at z=2.2. In the HS1700 field, we found a 5-sigma overdensity of eight SPIRE sources around 2.1 (~1.0 Mpc) from a density peak of LBGs at z=2.3. We did not find any significant overdensities in SSA22 field, but we found three 500 $mu$m sources are concentrated 3 (~1.4 Mpc) east to the LAEs overdensity. If all the SPIRE sources in these three overdensities are associated with protoclusters, the inferred star-formation rate densities are 10$^3$-10$^4$ times higher than the average value at the same redshifts. This suggests that dusty star-formation activity could be very strongly enhanced in z~2-3 protoclusters. Further observations are needed to confirm the redshifts of the SPIRE sources and to investigate what processes enhance the dusty star-formation activity in z~2-3 protoclusters.
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We present first results from the SXDF-ALMA 1.5 arcmin^2 deep survey at 1.1 mm using Atacama Large Millimeter Array (ALMA). The map reaches a 1sigma depth of 55 uJy/beam and covers 12 Halpha-selected star-forming galaxies at z = 2.19 or z=2.53. We have detected continuum emission from three of our Halpha-selected sample, including one compact star-forming galaxy with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M*/Msun)>10.9 whereas the other blue, main-sequence galaxies with log(M*/Msun)=10.0-10.8 are exceedingly faint, <290 uJy (2sigma upper limit). We also find the 1.1 mm-brightest galaxy, NB2315-02, to be associated with a compact (R_e=0.7+-0.1 kpc), dusty star-forming component. Given high gas fraction (44^{+20}_{-8}% or 37^{+25}_{-3}%) and high star formation rate surface density (126^{+27}_{-30} Msun yr^{-1}kpc^{-2}), the concentrated starburst can within less than 50^{+12}_{-11} Myr build up a stellar surface density matching that of massive compact galaxies at z~2, provided at least 19+-3% of the total gas is converted into stars in the galaxy centre. On the other hand, NB2315-07, which already has such a high stellar surface density core, shows a gas fraction (23+-8%) and is located in the lower envelope of the star formation main-sequence. This compact less star-forming galaxy is likely to be in an intermediate phase between compact dusty star-forming and quiescent galaxies.
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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.
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Until recently, only a handful of dusty, star-forming galaxies (DSFGs) were known at $z>4$, most of them significantly amplified by gravitational lensing. Here, we have increased the number of such DSFGs substantially, selecting galaxies from the uniquely wide 250-, 350- and 500-$mu$m Herschel-ATLAS imaging survey on the basis of their extremely red far-infrared colors and faint 350- and 500-$mu$m flux densities - ergo they are expected to be largely unlensed, luminous, rare and very distant. The addition of ground-based continuum photometry at longer wavelengths from the JCMT and APEX allows us to identify the dust peak in their SEDs, better constraining their redshifts. We select the SED templates best able to determine photometric redshifts using a sample of 69 high-redshift, lensed DSFGs, then perform checks to assess the impact of the CMB on our technique, and to quantify the systematic uncertainty associated with our photometric redshifts, $sigma=0.14,(1+z)$, using a sample of 25 galaxies with spectroscopic redshifts, each consistent with our color selection. For Herschel-selected ultrared galaxies with typical colors of $S_{500}/S_{250}sim 2.2$ and $S_{500}/S_{350}sim 1.3$ and flux densities, $S_{500}sim 50,$mJy, we determine a median redshift, $hat{z}_{rm phot}=3.66$, an interquartile redshift range, 3.30$-$4.27, with a median rest-frame 8$-$1000-$mu$m luminosity, $hat{L}_{rm IR}$, of $1.3times 10^{13},$L$_odot$. A third lie at $z>4$, suggesting a space density, $rho_{z>4}$, of $approx 6 times 10^{-7},$Mpc$^{-3}$. Our sample contains the most luminous known star-forming galaxies, and the most over-dense cluster of starbursting proto-ellipticals yet found.
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