The Rest-Frame Optical Spectra of SCUBA Galaxies

By A. M. Swinbank, I. Smail, S. Chapman, A. Blain, R. Ivison, William Keel. 2004

210 citations recorded by the source corpus.

We present near-infrared spectroscopy and narrowband imaging at the wavelength of redshifted Hα for a sample of 30 high-redshift, far-infrared luminous galaxies. This sample is selected from surveys in the submillimeter, millimeter, and radio wave bands and has complete redshift coverage with a median redshift of z ~ 2.4. We use our data to measure the Hα properties of these systems and to gauge the prevalence of active galactic nuclei (AGNs) in these galaxies through their [N II]/Hα ratios and Hα line widths. Removing obvious AGNs, we find that the predicted Hα star formation rates in this diverse population are suppressed (by a factor of ~10) compared to those derived from their far-infrared luminosities. Using the AGN indicators provided by our near-infrared spectra, we estimate that AGNs are present in at least 40% of the galaxies in our sample. To further investigate this, we construct a composite rest-frame spectrum for both the entire sample and those galaxies that individually show no signs of nuclear activity. We find [N II]/Hα ratios for both composite spectra that suggest that the energy output of the galaxies is star formation rather than AGN dominated. However, we also find that the Hα line in the composite non-AGN spectrum is best fitted with an underlying broad-line component with a narrow/broad flux ratio of 0.45 ± 0.20. The median Hα line width for our sample (removing obvious AGNs) is 400 ± 70 km s-1 (FWHM), and the typical spatial extent of the Hα emission in our narrowband observations is ≲4-8 kpc, which indicates a dynamical mass of (1-2) × 1011 M☉ with corresponding dynamical times of 10-20 Myr. Using both high-resolution imaging and spectroscopically identified velocity offsets, we find that seven of the far-infrared luminous galaxies have companions, suggesting that they are undergoing interactions/mergers, and from their relative velocities we can determine a dynamical mass of (1.5 ± 0.9) × 1011 M☉. These measurements are comparable to millimeter CO estimates for the dynamical masses of these systems on similar scales and larger than recent estimates of the dynamical masses of UV-selected galaxies at similar redshifts derived in an identical manner. Using the [N II]/Hα index to predict abundances, we investigate the luminosity-metallicity relation for these galaxies and find that many have metallicities consistent with UV-selected high-redshift galaxies and slightly lower than local luminous infrared and elliptical galaxies (although we caution that our metallicity estimates have possible systematic uncertainties). We also compared our Hα and far-infrared luminosities with deep Chandra observations of a subset of our survey fields and use these data to further assess their AGN content. We conclude that these high-redshift, far-infrared luminous galaxies represent a population of massive, metal-rich, merging systems with high instantaneous star formation rates, strong dust obscuration, and actively fueled AGNs that are likely to be the progenitors of massive local elliptical galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d3073ce0cd04f2a4cbdb1df01cc79158b6a7e47a

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In Astronomy and Astrophysics

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Citations in the corpus

• Mid-Infrared Spectral Diagnosis of Submillimeter Galaxies (2007, background): “Furthermore, AGN indicators at UVand optical wavelengths can be very obscured in dusty SMGs (Swinbank et al. 2004; Chapman et al. 2005).”
• The X-Ray Spectral Properties of SCUBA Galaxies (2005, background): “Under this assumption the X-ray– derived star formation rates ( 1300–2700M yr 1) are in good agreement with those determined using other techniques (e.g., Swinbank et al. 2004; Chapman et al. 2005).”
• A Highly Complete Spectroscopic Survey of the GOODS-N Field (2008, background): “In addition, Reddy et al. (2006) gave a substantial sample of color-selected redshifts, Chapman et al. (2004, 2005) and Swinbank et al. (2004) presented a small number of radio/submillimeter redshifts, and Treu et al. (2005) measured redshifts for a sample of spheroids.”
• AN ALMA SURVEY OF SUBMILLIMETER GALAXIES IN THE EXTENDED CHANDRA DEEP FIELD SOUTH: THE REDSHIFT DISTRIBUTION AND EVOLUTION OF SUBMILLIMETER GALAXIES (2013, methodology): “Crucially our estimate of the dynamical mass is consistent with spectroscopic studies of resolved Hα or 12CO emission lines, which demonstrate that SMGs typically have dynamical masses of 1–2× 1011M⊙ (Swinbank et al. 2004; Alaghband-Zadeh et al. 2012; Bothwell et al. 2013), inside a 5 kpc radius.”
• Dynamical Properties of z ~ 2 Star-forming Galaxies and a Universal Star Formation Relation (2007, background): “SMGs are more compact and at the same time have greater velocity widths (as in Swinbank et al. 2004) than the UV/optically selected galaxies (by a factor of 2 in each coordinate; Greve et al. 2005; Tacconi et al. 2006; Iono et al. 2006).”
• A survey of molecular gas in luminous sub-millimetre galaxies (2012, methodology): “…selected to have precise spectroscopic redshifts, derived using one or more of the following techniques: (i) Lyman α emission (C05); (ii) Hα emission (Swinbank et al. 2004) and (iii) polycyclic aromatic hydrocarbon emission from mid-IR spectroscopy with Spitzer (Pope et al. 2008;…”
• An ALMA survey of sub-millimetre Galaxies in the Extended Chandra Deep Field South: the far-infrared properties of SMGs (2013, unknown): “…of star forming galaxies (across several galaxy types) from the SINGS survey from Draine et al. (2007) (see also Scoville 2013) is δGDR =130± 20 for galaxies with metallicities above Z /Z∼ < > ∼ 0.2 (which is likely to represent a lower-limit for SMGs; Swinbank et al. 2004; Takata et al. 2006).”
• TOWARD THE STANDARD POPULATION SYNTHESIS MODEL OF THE X-RAY BACKGROUND: EVOLUTION OF X-RAY LUMINOSITY AND ABSORPTION FUNCTIONS OF ACTIVE GALACTIC NUCLEI INCLUDING COMPTON-THICK POPULATIONS (2014, methodology): “We basically refer to the redshift catalog provided by Trouille et al. (2008), which contains the results from previous works including Barger et al. (2003), Swinbank et al. (2004), Chapman et al. (2005), and Reddy et al. (2006).”
• Dusty Star Forming Galaxies at High Redshift (2014, background): “The first comprehensive rest-frame optical study of SMGs was done by Swinbank et al. (2004) who spectroscopically confirm 30 galaxies in Hα emission whose redshifts were originally reported via detection of Lyα in Chapman et al. (2003a) and Chapman et al. (2004b).”
• Spitzer Power-Law Active Galactic Nucleus Candidates in the Chandra Deep Field-North (2007, background): “…galaxies have secure spectroscopic redshifts (Barger et al. 2001, 2002, 2003; Hornschemeier et al. 2001; Dawson et al. 2003; Cowie et al. 2004; Swinbank et al. 2004; Wirth et al. 2004 [Team Keck Redshift Survey]; Chapman et al. 2005; the Sloan Digital Sky Survey [SDSS]) and 2 additional…”
• EXTRAGALACTIC MILLIMETER-WAVE SOURCES IN SOUTH POLE TELESCOPE SURVEY DATA: SOURCE COUNTS, CATALOG, AND STATISTICS FOR AN 87 SQUARE-DEGREE FIELD (2009, background): “…(see Blain et al. (2002) for a review) indicate that: (1) they have dynamical masses of ∼1011 M and total far-infrared luminosities of ∼1013 L (Swinbank et al. 2004; Greve et al. 2005; Chapman et al. 2005; Kovács et al. 2006; Pope et al. 2006); (2) they are forming stars prodigiously at…”
• WHAT DOES A SUBMILLIMETER GALAXY SELECTION ACTUALLY SELECT? THE DEPENDENCE OF SUBMILLIMETER FLUX DENSITY ON STAR FORMATION RATE AND DUST MASS (2010, unknown): “Swinbank et al. 2004; Greve et al. 2005; Tacconi et al. 2006, 2008; Bouché et al. 2007; Biggs & Ivison 2008; Capak et al. 2008; Younger et al. 2008, 2010; Iono et al. 2009; Engel et al. 2010).”
• Gas metallicity diagnostics in star-forming galaxies (2006, background): “…beyond z = 1, such as Lyman-break galaxies (e.g., Teplitz et al. 2000a, 2000b; Pettini et al. 2001), submillimeter-selected high-z galaxies (Swinbank et al. 2004), and so on (see also, e.g., Kobulnicky & Kewley 2004; Savaglio et al. 2005; Maier et al. 2006; Liang et al. 2006; Erb et al.…”
• Testing the evolutionary link between submillimetre galaxies and quasars: CO observations of QSOs at z∼ 2 (2008, methodology): “These systems have ULIRG-like bolometric luminosities, LIR ≥ 10 12 L⊙ (Kovács et al. 2006; Coppin et al. 2008), and they have many of the properties expected for gas-rich mergers (Swinbank et al. 2004, 2006; Tacconi et al. 2006).”
• An interferometric CO survey of luminous submillimetre galaxies (2005, methodology): “…of submm flux isbelieved to be due their higher dust temperatures (Blain et al.2004a; Chapman et al. 2005), have similar gas masses as classical SMGs (Swinbank et al. 2004; Smail et al. 2004), this would double our current estimate of the abundance of massive baryonic galaxies t high redshifts.”
• The formation of high-redshift submillimetre galaxies (2009, background): “SMGs are extremely massive, with typical ∼5 × 1011 M bulges in place (Swinbank et al. 2004; Borys et al. 2005), and are a highly clustered population of galaxies, residing in ∼1012–1013 M dark matter haloes (Blain et al. 2004; Swinbank et al. 2008).”