HerMES: THE REST-FRAME UV EMISSION AND A LENSING MODEL FOR THEz= 6.34 LUMINOUS DUSTY STARBURST GALAXY HFLS3

Abstract

We discuss the rest-frame ultraviolet emission from the starbursting galaxy HFLS3 at a redshift of 6.34. The galaxy was discovered in Herschel/SPIRE data due to its red color in the sub-mm wavelengths from 250 to 500 µm. The apparent instantaneous star-formation rate of HFLS3 inferred from the total far-IR luminosity measured with over 15 photometric data points between 100 and 1000 µm is 2900 M ⊙ yr −1 . Keck/NIRC2 K s -band adaptive optics imaging data showed two potential near-IR counterparts near HFLS3. Previously, the northern galaxy was taken to be in the foreground at z = 2.1 while the southern galaxy was assumed to HFLS3's near-IR counterpart. The recently acquired Hubble/WFC3 and ACS imaging data show conclusively that both optically-bright galaxies are in the foreground at z < 6. A new lensing model based on the Hubble imaging data and the mm-wave continuum emission yields a magnification factor of 2.2 ± 0.3. The lack of multiple imaging constrains the lensing magnification to be lower than either 2.7 or 3.5 at the 95% confidence level for the two scenarios, which attribute one or two components to HFLS3 in the source plane. Once accounting for the possibility of gravitational lensing, the instantaneous star-formation rate is 1320 M ⊙ yr −1 with the 95% confidence lower limit around 830 M ⊙ yr −1 . Using models for the rest-frame UV to far-IR spectral energy distribution (SED) we determine the average star-formation rate over the last 100 Myr to be around 660 M ⊙ yr −1 . The dust and stellar masses of HFLS3 from the same SED models are at the level of 3 × 10 8 M ⊙ and ∼ 5 × 10 10 M ⊙ , respectively, with large systematic uncertainties on assumptions related to the SED model. With Hubble/WFC3 images we also find diffuse near-IR emission about 0.5 arcseconds (∼ 3 kpc) to the South-West of HFLS3 that remains undetected in the ACS imaging data. The emission has a photometric redshift consistent with either z ∼ 6 or a dusty galaxy template at z ∼ 2. If at the same redshift as HFLS3 the detected diffuse emission could be part of the complex merger system that could be triggering the starburst. Alternatively, it could be part of the foreground structure at z ∼ 2.1 that is responsible for lensing of HFLS3.

INFERRED Hα FLUX AS A STAR FORMATION RATE INDICATOR AT z ∼ 4–5: IMPLICATIONS FOR DUST PROPERTIES, BURSTINESS, AND THE z = 4–8 STAR FORMATION RATE FUNCTIONS

“…Current observational constraints on the IR-to-UV luminosity ratio as a function of the UV continuum slope (β) using stacks of UV-selected galaxies (left panel) and constraints on individual galaxies from ALMA and PdBI (right panel). While the stacking results by Coppin et al (2015) over the redshift rangez 35 -are in good agreement with the dust calibration needed to bring Hα-and UV-based SFR measurements, i.e., b =+ A 1.99 2.5 1600 () (see Section 5.1), many of the results suggest lower dust corrections (Cooray et al 2014;Capak et al 2015;Schaerer et al 2015;Watson et al 2015;Álvarez-Márquez et al 2016;Bouwens et al 2016a). At present, the impact that dust has on the observed UV brightness and SFRs of z∼4-5 galaxies is not clear, on the basis of far-IR observations.…”

HerMES: ALMA IMAGING OFHERSCHEL-SELECTED DUSTY STAR-FORMING GALAXIES

“…However, there are also two objects with multiple sources that have separations smaller than 1″, which have summed flux densities comparable to this; namely HADFS02 (16.8 mJy) and HECDFS13 (15.3 mJy). This is approaching the values found in the most extreme systems, such as GN20 (20.6 mJy, Pope et al 2006) and HFLS3 (15-20 mJy; Riechers et al 2013;Cooray et al 2014;Robson et al 2014). It is a level that is extremely difficult to reproduce in simulations (e.g., Narayanan et al 2010).…”

Galaxy Evolution in the Radio Band: The Role of Star-forming Galaxies and Active Galactic Nuclei

“…Solid lines refer to the global SFR function based on (dust-corrected) UV plus far-IR measurements, while dashed lines are the SFR functions of galaxies hosting an AGN with X-ray luminosity larger than 10 42 erg s −1 . UV data (open symbols) are from van der Burg et al (2010; diamonds), Bouwens et al (2015;pentagons) and Finkelstein et al (2015; inverse triangles), Cucciati et al (2012;triangles), and Wyder et al (2005;crosses); far-IR data from Gruppioni et al (2015;hexagons), Magnelli et al (2013;circles), Gruppioni et al (2013;squares), Lapi et al (2011;stars), and Cooray et al (2014;pacmans). Fig.…”