Evidence for Extended, Obscured Starbursts in Submillimeter Galaxies

By S. Chapman, I. Smail, R. Windhorst, T. Muxlow, R. Ivison. 2004

158 citations recorded by the source corpus.

We compare high-resolution optical and radio imaging of 12 luminous submillimeter galaxies at a median z = 2.2 ± 0.2 observed with the Hubble Space Telescope (HST) and the MERLIN and Very Large Array (VLA) radio interferometers at comparable spatial resolution, ~0.″3 (~2 kpc). The radio emission is used as a tracer of the likely far-IR morphology of these dusty, luminous galaxies. In ~30% of the sample the radio emission appears unresolved at this spatial scale, suggesting that the power source is compact and may be either an obscured active galactic nucleus or a compact nuclear starburst. However, in the majority of the galaxies (8/12; ~70%), we find that the radio emission is resolved by MERLIN/VLA on scales of ~1'' (~10 kpc). For these galaxies we also find that the radio morphologies are often broadly similar to their rest-frame-UV emission traced by our HST imaging. To assess whether the radio emission may be extended on even larger scales (≫1'') resolved out by the MERLIN+VLA synthesized images, we compare VLA B-array (5'' beam) to VLA A-array (1.″5 beam) fluxes for a sample of 50 μJy radio sources, including five submillimeter galaxies. The submillimeter galaxies have comparable fluxes at these resolutions, and we conclude that the typical radio-emitting region in these galaxies is unlikely to be much larger than ~1'' (~10 kpc). We discuss the probable mechanisms for the extended emission in these galaxies and conclude that their luminous radio and submillimeter emission arises from a large, spatially extended starburst. The median star formation rates for these galaxies are ~1700 M☉ yr-1 (M > 0.1 M☉), occurring within regions with typical sizes of ~40 kpc2 and giving a star formation density of 45 M☉ yr-1 kpc-2. Such vigorous and extended starbursts appear to be uniquely associated with the submillimeter population. A more detailed comparison of the distribution of UV and radio emission in these systems shows that the broad similarities on large scales are not carried through to smaller scales, where there is rarely a one-to-one correspondence between the structures seen in the two wave bands. We interpret these differences as resulting from highly structured internal obscuration within the submillimeter galaxies, suggesting that their vigorous activity is producing windblown channels through their obscuring dust clouds. If correct, this underlines the difficulty of using UV morphologies to understand structural properties of this population and also may explain the surprising frequency of Lyα emission in the spectra of these very dusty galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/52069209a34681a1cc77443cff6a2a3f41f7b665

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. R. Dav'e
4. D. Narayanan
5. R. Somerville
6. D. M. Alexander
7. Thomas J. Cox
8. T. Naab

In Instrumentation

1. P. Hopkins
2. L. Hernquist
3. M. Cappellari
4. R. Dav'e
5. C. Conroy
6. R. Somerville
7. Thomas J. Cox
8. D. Narayanan

Citations in the corpus

• On the fraction of star formation occurring in bound stellar clusters (2012, background): “Indeed, observations of high-redshift galaxies show that the gas densities (102– 105 M pc−2) and SFRs (20–3000 M yr−1) commonly reached extreme values in the early Universe that are presently rare (e.g. Chapman et al. 2004; Solomon & Vanden Bout 2005; Daddi et al. 2007; Genzel et al. 2010).”
• Dusty Star Forming Galaxies at High Redshift (2014, methodology): “Chapman et al. (2004a) summarizes the results of the first search of thewarm-dust analog of SMGs as Optically Faint Radio Galaxies (OFRGs).”
• A 158 μm [C ii] LINE SURVEY OF GALAXIES AT z ∼ 1–2: AN INDICATOR OF STAR FORMATION IN THE EARLY UNIVERSE (2010, background): “Interferometric measurements of z ∼ 1–3 SMGs in the radio continuum have detected emission over kpc scales (Chapman et al. 2004), with a median size ∼5 kpc (Biggs & Ivison 2008), and interferometric CO observations of a sample of z ∼ 2 SMGs show emission over scales ∼4 kpc (Tacconi et al. 2006,…”
• Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly (2009, background): “Such extreme SFRs likely result from major mergers (e.g. Chapman et al., 2004; Swinbank et al., 2004; Greve et al., 2005; Tacconi et al., 2006, 2008; Younger et al., 2007, 2008; Berciano Alba et al., 2010; Narayanan et al., 2009, 2010) and cannot be sustained for a long period (after a few hundred…”
• THE STELLAR MASS CONTENT OF SUBMILLIMETER-SELECTED GALAXIES (2010, background): “To test the origin we need to distinguish the nearIR emission from the galaxies’ nuclei from that which follows the obscured star formation (which may be more distributed; see, e.g., Chapman et al. 2004; Biggs & Ivison 2008; Menéndez-Delmestre et al. 2009).”
• The LABOCA survey of the Extended Chandra Deep Field South: A photometric redshift survey of submillimetre galaxies (2010, methodology): “We note that these values of AV are integrated across the whole galaxy and that the obscuration in the regions responsible for the majority of the FIR/submillimetre emission is considerably larger (e.g. Chapman et al. 2004b; Takata et al. 2006; Ivison et al. 2010b).”
• THE PHYSICS OF THE FAR-INFRARED–RADIO CORRELATION. I. CALORIMETRY, CONSPIRACY, AND IMPLICATIONS (2009, background): “Many starbursts at high redshifts are observed to be kiloparsecs in radius instead of ∼ 100 pc (e.g., Chapman et al. 2004; Biggs & Ivison 2008; Younger et al. 2008), usually with moderate Σg but at least one with a surface density comparable to Arp 220 (Walter et al. 2009).”
• Radiation Pressure-supported Starburst Disks and Active Galactic Nucleus Fueling (2005, background): “It remains to be seen if the same is true in their highredshift counterparts (Chapman et al. 2004 find radio sizes of ∼ 3 kpc in several systems, suggesting that star formation may be more extended in some high redshift ULIRGs).”
• Evidence for a Population of High-Redshift Submillimeter Galaxies from Interferometric Imaging (2007, background): “…measurements of the angular extent of the millimeter (Downes et al. 1999; Genzel et al. 2003; Downes & Solomon 2003; Kneib et al. 2005; Tacconi et al. 2006) and submillimeter (Iono et al. 2006) emission from SMGs, and marginally with those of the radio continuum (Chapman et al. 2004).”
• The n ature of submillimetre galaxies in cosmological hydrodynamic simulations (2009, background): “This may argue against the major merger interpretation, since in mergers the star-forming gas is generally driven into a very compact and highly obscured nuclear starburst that in local ULIRGs are .”
• A Redshift Survey of the Submillimeter Galaxy Population (2004, methodology): “For example, a comparison of the UV and long-wavelength morphologies of SMGs indicates that their star formation is more spatially extended than in the local population of ULIRGs (Chapman et al. 2004b), likely resulting in differences in the physical conditions experienced by dust grains (Lu et al. ”
• The formation of high-redshift submillimetre galaxies (2009, background): “Selected for their prodigious long wavelength emission ( 5 mJy at 850 μm), SMGs are thought to be starburst dominated (Chapman et al. 2004; Alexander et al. 2008; Younger et al. 2008a), and have massive ∼1010–1011 M H2 gas reservoirs (Greve et al. 2005; Tacconi et al. 2006, 2008).”
• The Hubble Deep Field North SCUBA Super-map - III. Optical and near-infrared properties of submillimetre galaxies (2005, background): “1 shows how consistent the photometric redshifts are for those sub-mm sources that have spectroscopic redshifts in the Cowie et al. (2004) catalogue or the newer Chapman et al. (2004) paper.”
• A physical model for z∼ 2 dust-obscured galaxies (2009, background): “…absorption of stellar light by cold clouds (Narayanan et al. 2010), and are generally thought to have their bolometric luminosity powered by star formation (Chapman et al. 2004; Alexander et al. 2005; Valiante et al. 2007; Pope et al. 2008a; Younger et al. 2008a; Menéndez-Delmestre et al. 2009).”
• A semi-empirical simulation of the extragalactic radio continuum sky for next generation radio telescopes (2008, background): “This reflects the fact that local starbursts are compact (kpc-scale) whereasz ∼ 2 sub-mm galaxies are an order of magnitude larger in scale (see e.g. MERLIN interferometry, Chapman et al. 2004).”
• Molecular Gas at High Redshift (2005, background): “There is also indirect evidence of extended, large molecular gas disks from measurement of extended nonthermal radio continuum (Chapman et al. 2004) and, by implication, extended FIR and CO emission based on the radio-FIR correlation (Carilli, Menten & Yun 1999).”
• THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0–8 (2012, result): “This in turn translates to a high star formation rate, on the order of 200-1000M⊙ yr−1, which is consistent with observations of ultra-luminous infrared galaxies (ULIRGs; Magnelli et al. 2012; Michałowski et al. 2010a,b; Daddi et al. 2005; Chapman et al. 2004).”
• The Link between Submillimetre Galaxies and Luminous Ellipticals: Near-Infrared IFU Spectroscopy of Submillimetre Galaxies (2006, background): “Component A is the radio counterpart in the 1.4-GHz map from Chapman et al. (2004).”