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Register a new userHerschel reveals the obscured star formation in HiZELS Halpha emitters at z=1.47
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We describe the far-infrared (FIR; rest-frame 8--1000mu m) properties of a sample of 443 Halpha-selected star-forming galaxies in the COSMOS and UDS fields detected by the HiZELS imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Halpha (and [OII] if available) emitters in a narrow redshift slice at z = 1.47+/-0.02. We use a stacking approach in Spitzer, Herschel (from PEP and HerMES surveys) and AzTEC images to describe their typical FIR properties. We find that HiZELS galaxies with observed Halpha luminosities of ~ 10^{8.1-9.1} Lo have bolometric FIR luminosities of typical LIRGs, L_FIR ~ 10^{11.48+/-0.05} Lo. Combining the Halpha and FIR luminosities, we derive median SFR = 32+/-5 Mo/yr and Halpha extinctions of A(Halpha) = 1.0+/-0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M*) to A(Halpha) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies, we provide an empirical parametrisation of the SFR as a function of (u-z)_rest colours and 3.6mu m photometry. We find that the observed Halpha luminosity is a dominant SFR tracer when (u-z)_rest ~< 0.9 mag or when 3.6mu m photometry > 22 mag (Vega) or when M* < 10^9.7 Mo. We do not find any correlation between the [OII]/Halpha and FIR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions. The luminosity-limited HiZELS sample tends to lie above of the so-called `main sequence for star-forming galaxies, especially at low M*. This work suggests that obscured star formation is linked to the assembly of M*, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.
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We obtained Subaru FMOS observations of Halpha emitting galaxies selected from the HiZELS narrow-band survey, to investigate the relationship between stellar mass, metallicity and star-formation rate at z = 0.84 - 1.47, for comparison with the Fundamental Metallicity Relation seen at low redshift. Our findings demonstrate, for the first time with a homogeneously selected sample, that a relationship exists for typical star-forming galaxies at z = 1 - 1.5 and that it is surprisingly similar to that seen locally. Therefore, star-forming galaxies at z = 1 - 1.5 are no less metal abundant than galaxies of similar mass and star formation rate (SFR) at z = 0.1, contrary to claims from some earlier studies. We conclude that the bulk of the metal enrichment for this star-forming galaxy population takes place in the 4 Gyr before z = 1.5. We fit a new mass-metallicity-SFR plane to our data which is consistent with other high redshift studies. However, there is some evidence that the mass-metallicity component of this high redshift plane is flattened, at all SFR, compared with z = 0.1, suggesting that processes such as star-formation driven winds, thought to remove enriched gas from low mass halos, are yet to have as large an impact at this early epoch. The negative slope of the SFR-metallicity relation from this new plane is consistent with the picture that the elevation in the SFR of typical galaxies at z > 1 is fuelled by the inflow of metal-poor gas and not major merging.
We use deep, five band (100-500um) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFR_FIR, of galaxies in the Bullet cluster (z=0.296), and a smaller background system (z=0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFR_FIR = 144 +/- 14 M_sun yr^-1. On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFR_FIR (21 galaxies; 207 +/- 9 M_sun yr^-1). SFRs extrapolated from 24um flux via recent templates (SFR_24) agree well with SFR_FIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR_24 underestimates SFR_FIR due to a significant excess in observed S_100/S_24 (rest frame S_75/S_18) compared to templates of the same FIR luminosity.
New results are presented, as part of the Hi-z Emission Line Survey (HiZELS), from the largest area survey to date (1.4 sq.deg) for Lyman-alpha emitters (LAEs) at z~9. The survey, which is primarily targeting H-alpha emitters at z<3, uses the Wide Field CAMera on the United Kingdom Infrared Telescope and a custom narrow-band filter in the J band and reaches a Lyman-alpha luminosity limit of ~10^43.8 erg/s over a co-moving volume of 1.12x10^6 Mpc^3 at z=8.96+-0.06. Only 2 candidates were found out of 1517 line emitters and those were rejected as LAEs after follow-up observations. The limit on the space density of bright LAEs is improved by 3 orders of magnitude, consistent with suppression of the bright end of the Lyman-alpha luminosity function beyond z~6. Combined with upper limits from smaller but deeper surveys, this rules out some of the most extreme models for high-redshift LAEs. The potential contamination of future narrow-band Lyman-alpha surveys at z>7 by Galactic brown dwarf stars is also examined, leading to the conclusion that such contamination may well be significant for searches at 7.7<z<8.0, 9.1<z<9.5 and 11.7 < z < 12.2.
New results from a large survey of H-alpha emission-line galaxies at z=0.84 using WFCAM/UKIRT and a custom narrow-band filter in the J band are presented as part of the HiZELS survey. Reaching an effective flux limit of 1e-16 erg/s/cm^2 in a comoving volume of 1.8e5 Mpc^3, this represents the largest and deepest survey of its kind ever done at z~1. There are 1517 potential line emitters detected across 1.4 sq.deg of the COSMOS and UKIDSS UDS fields, of which 743 are selected as H-alpha emitters. These are used to calculate the H-alpha luminosity function, which is well-fitted by a Schechter function with phi*=10^(-1.92+-0.10) Mpc^-3, L*=10^(42.26+-0.05)erg/s, and alpha=-1.65+-0.15. The integrated star formation rate density (SFRD) at z=0.845 is 0.15+-0.01 M_sun/yr/Mpc^3. The results robustly confirm a strong evolution of SFRD from the present day out to z~1 and then flattening to z~2, using a single star-formation indicator. Out to z~1, both the characteristic luminosity and space density of the H-alpha emitters increase significantly; at higher redshifts, L* continues to increase, but phi* decreases. The z=0.84 H-alpha emitters are mostly disk galaxies (82+-3%), while 28+-4% of the sample show signs of merger activity and contribute ~20% to the total SFRD. Irregulars and mergers dominate the H-alpha luminosity function above L*, while disks are dominant at fainter luminosities. These results demonstrate that it is the evolution of normal disk galaxies that drives the strong increase in the SFRD from the current epoch to z~1, although the continued strong evolution of L* beyond z=1 suggests an increasing importance of merger activity at higher redshifts.
Ly-alpha emitters (LAEs) are seen everywhere in the redshift domain from local to z~7. Far-infrared (FIR) counterparts of LAEs at different epochs could provide direct clues on dust content, extinction, and spectral energy distribution (SED) for these galaxies. We search for FIR counterparts of LAEs that are optically detected in the GOODS-North field at redshift z~2.2 using data from the Herschel Space Telescope with the Photodetector Array Camera and Spectrometer (PACS). The LAE candidates were isolated via color-magnitude diagram using the medium-band photometry from the ALHAMBRA Survey, ancillary data on GOODS-North, and stellar population models. According to the fitting of these spectral synthesis models and FIR/optical diagnostics, most of them seem to be obscured galaxies whose spectra are AGN-dominated. From the analysis of the optical data, we have observed a fraction of AGN or composite over source total number of ~0.75 in the LAE population at z~2.2, which is marginally consistent with the fraction previously observed at z=2.25 and even at low redshift (0.2<z<0.45), but significantly different from the one observed at redshift ~3, which could be compatible either with a scenario of rapid change in the AGN fraction between the epochs involved or with a non detection of obscured AGN in other z=2-3 LAE samples due to lack of deep FIR observations. We found three robust FIR (PACS) counterparts at z~2.2 in GOODS-North. This demonstrates the possibility of finding dust emission in LAEs even at higher redshifts.
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