MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES

By K. Men'endez-Delmestre, A. Blain, I. Smail, D. M. Alexander, S. Chapman, Lee Armus, D. Frayer, R. Ivison, H. Teplitz. 2009

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We used the Spitzer Infrared Spectrograph (IRS) to study the mid-IR properties and investigate the energetics of 24 Submillimeter Galaxies (SMGs). This is the largest sample of SMGs observed with Spitzer IRS and covers the full extent of properties of the radio-identified population of SMGs in the redshift range of z ∼ 0.65–3.2. We observe broad emission features from polycyclic aromatic hydrocarbons in more than 80% of our sample. We find that the median mid-IR spectrum is well described by a starburst component with an additional power law, Fν ∼ ν−2, likely representing a <32% contribution from an active galactic nucleus to the bolometric luminosity. Our results thus confirm that starburst activity dominates the bolometric luminosity in SMGs. We find that SMGs show weaker silicate absorption at ∼9.7 μm than local ULIRGs. We also find stronger 6.2-μm PAH emission in SMGs (relative to the 7.7 μm PAH feature) than in local nuclear starbursts, which may be attributed to lower extinction by ice along the line of sight to SMGs. This suggests that the continuum and PAH emitting regions of SMGs are less obscured than in local starbursts and similarly luminous low-redshift ULIRGs. We interpret these results as evidence for a more extended distribution of cool and warm dust in SMGs compared to the more compact emitting regions in local ULIRGs and starbursts. Together these results suggest that SMGs are not simple high-redshift analogs of nuclear starbursts or local ULIRGs, but instead they appear to have star formation which resembles that seen in less-extreme star-forming environments at z ∼ 0–suggesting their intense activity is distributed across a far larger region than the ∼1 kpc nuclear bursts in local ULIRGs.

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1. P. Hopkins
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Citations in the corpus

• WHAT DOES A SUBMILLIMETER GALAXY SELECTION ACTUALLY SELECT? THE DEPENDENCE OF SUBMILLIMETER FLUX DENSITY ON STAR FORMATION RATE AND DUST MASS (2010, background): “…L ; e.g., Kovács et al. 2006), high-redshift (Chapman et al. 2005) galaxies powered primarily by star formation rather than active galactic nuclei (AGNs; Alexander et al. 2005a, 2005b, 2008; Valiante et al. 2007; Menéndez-Delmestre et al. 2007, 2009; Pope et al. 2008; Younger et al. 2008, 2009b).”
• A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies (2017, background): “…Magnelli et al. 2011), and a number of works have already shown that local LIRGs (and not ULIRGs) are probably the closest local analogs of this high-z, IR-bright galaxy population (Desai et al. 2007; Pope et al. 2008; Menéndez-Delmestre et al. 2009; Dı́az-Santos et al. 2010b; Stacey et al. 2010).”
• Dusty Star Forming Galaxies at High Redshift (2014, background): “Interestingly, Menéndez-Delmestre et al. (2009) find that the ratio between 6.2 and 7.7 µm PAH emission is higher than in local ULIRGs or nuclear starbursts, pointing to a more extended distribution of both cool and warm dust in SMGs than in compact local ULIRGs.”
• The LABOCA survey of the Extended Chandra Deep Field South: A photometric redshift survey of submillimetre galaxies (2010, background): “Studies of mid-IR spectra of SMGs have shown that they are similar to M82 with an additional power-law contribution, potentially due to AGN emission or hot dust (Menéndez-Delmestre et al. 2007, 2009; Pope et al. 2008; Coppin et al. 2010b).”
• Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly (2009, methodology): “…established that on average AGN activity is responsible for at most ∼ 10–20% of the bolometric infrared emission of SMGs (Alexander et al., 2005, 2008; Menéndez-Delmestre et al., 2007, 2009; Valiante et al., 2007; Pope et al., 2008; Hainline et al., 2009; Murphy et al., 2009; Watabe et al., 2009).”
• MOST SUBMILLIMETER GALAXIES ARE MAJOR MERGERS (2010, background): “…Auf dem Hügel 71, 53121 Bonn, Germany 9CNRS and Institut d’Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France 2007; Pope et al. 2008; Menéndez-Delmestre et al. 2009) spectroscopic work has shown that starbursts are the primary power source, with AGN present in a large…”
• THE STELLAR MASS CONTENT OF SUBMILLIMETER-SELECTED GALAXIES (2010, methodology): “…and mid-IR spectra of SMGs indicate that the majority of the population are not dominated by an active nucleus (AGN), many SMGs host AGN activity (Alexander et al. 2003, 2005; Pope et al. 2008; Menéndez-Delmestre et al. 2009), which may not be negligible for the purpose of stellar mass studies.”
• A Herschel view of the far-infrared properties of submillimetre galaxies (2012, background): “…star-forming regions than in local ULIRGs (Tacconi et al. 2006, 2008, 2010) and by the observations of strong PAH signatures in their IRS spectra (Lutz et al. 2005; Valiante et al. 16 Magnelli et al.: Far-infrared properties of SMGs 2007; Pope et al. 2008; Menéndez-Delmestre et al. 2007, 2009).”
• Deep multi-frequency radio imaging in the Lockman Hole using the GMRT and VLA (2009, methodology): “Different approaches have been used to measure the actual AGN contribution; spectroscopic/photometric mid-IR diagnostics (e.g. Menéndez-Delmestre et al. 2009), high resolution radio imaging (e.g. Biggs & Ivison 2008), X-ray detections/stacking (e.g. Alexander et al. 2003), and deviations from the…”
• THE SCUBA-2 COSMOLOGY LEGACY SURVEY: ALMA RESOLVES THE REST-FRAME FAR-INFRARED EMISSION OF SUB-MILLIMETER GALAXIES (2014, background): “Limited studies in the radio and CO also hint that SMGs have sizes of a few kpc in diameter (see Menéndez-Delmestre et al. (2009) for a discussion of the mid–infrared sizes of SMGs).”
• The stellar masses and specific star-formation rates of submillimetre galaxies (2011, background): “%) contamination of their bolometric luminosities by active galactic nuclei (AGNs; Alexander et al. 2005, 2008; Menéndez-Delmestre et al. 2007, 2009; Valiante et al. 2007; Pope et al. 2008; Hainline et al. 2009; Murphy et al. 2009; Watabe et al. 2009, M10).”
• Far-infrared spectral energy distribution fitting for galaxies near and far (2012, background): “The mid-infrared spectra of dusty starbursts have been shown to vary substantially at both low-z and high-z (Brandl et al. 2006; Pope et al. 2008; Menéndez-Delmestre et al. 2009).”
• Star formation rates and masses of z∼ 2 galaxies from multicolour photometry (2010, background): “They certainly exist, and can lead to real giant starbursts bringing galaxies to SFRs as high as ∼ 1000 M⊙/yr, currently identified with SMGs (e.g. Tacconi et al. 2008; Menendez-Delmestre et al. 2009).”
• 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).”
• An ALMA survey of the SCUBA-2 CLS UDS field: physical properties of 707 sub-millimetre galaxies (2019, background): “However, the limited mid-infrared spectroscopy available for SMGs indicates that most do not show silicate absorption as strong as seen in Arp 220 (Farrah et al. 2008; Menéndez-Delmestre et al. 2009).”
• AN ALMA SURVEY OF SUB-MILLIMETER GALAXIES IN THE EXTENDED CHANDRA DEEP FIELD SOUTH: PHYSICAL PROPERTIES DERIVED FROM ULTRAVIOLET-TO-RADIO MODELING (2015, background): “Menéndez-Delmestre et al. (2009) also find some variation of the ratios of different PAH features from SMG to SMG that we are not able to reproduce using our fixed template, however due to the lack of data sampling the (rest-frame) mid-infrared emission for our SMGs in detail, we would not be able…”
• GOODS–Herschel: an infrared main sequence for star-forming galaxies (2011, methodology): “Finally, we applied this technique to a sample of submillimeter galaxies (SMGs) from Menendez-Delmestre et al. (2009) and Pope et al. (2008a).”