The properties of the interstellar medium within a star-forming galaxy at z= 2.3

By A. Danielson, A. M. Swinbank, I. Smail, P. Cox, A. Edge, A. Weiss, A. Harris, A. Baker, C. De Breuck, James E. Geach and 22 more. Monthly notices of the Royal Astronomical Society, 2010

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We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and submillimetre from the lensedz = 2.3 submillimetre galaxy SMM J2135−0102. We obtain very high signal-to-noise ratio detections of 11 transitions from three species and limits on a further 20 transitions from nine species. We use the 12 CO, [C I] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry and find strong evidence for a two-phase medium within this high-redshift starburst galaxy, comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing a suite of photodissociation region models, we show that on average the molecular gas is exposed to an ultraviolet (UV) radiation field that is ∼1000 times more intense than the Milky Way, with star-forming regions having a characteristic density of n ∼ 10 4 cm −3 . Thus, the average ISM density and far-UV radiation field intensity are similar to those found in local ultraluminous infrared galaxies (ULIRGs) and to those found in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12 CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic-ray flux within clouds, likely as a result of high star formation density. We find tentative evidence of a factor of ∼4 temperature range within the system. We expect that such internal structures are common in high-redshift ULIRGs but are missed due to the poor signal-to-noise ratio of typical observations. We show that, when integrated over the galaxy, the gas and star formation surface densities appear to follow the Kennicutt–Schmidt relation, although by comparing our data to high-resolution submillimetre imaging, our data suggest that this relation breaks down on scales of <100 pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z ∼ 2.3 at a level of detail that has only recently become possible at z < 0.1 and show the potential physical properties that will be studied in unlensed galaxies when the Atacama Large Millimeter Array is in full operation.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8cd474af9f15f5d03bd25a6ededc9b8e1bc6d750

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Citations in the corpus

THE INTERSTELLAR MEDIUM IN DISTANT STAR-FORMING GALAXIES: TURBULENT PRESSURE, FRAGMENTATION, AND CLOUD SCALING RELATIONS IN A DENSE GAS DISK AT z = 2.3 (2011, methodology): “2& 3 show that the lowest velocity material in Danielson et al. (2011),“Z1” and “Z2” (at ∆v=28±9 and -167±9km s−1 with respect to the systemic respectively) appear to relate to two clumps separated by < 0.2′′ in projection on the sky, are associated with the rest-frame 260-µm emission closest to…”
HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS (2010, background): “Furthermore Danielson et al. (2010) noted that the denser molecular gas tracers (such as high-J CO lines) have more peaked spectra, while lower-density tracers have smoother spectra (Greve et al. 2005 also found relatively smooth low-J spectra in SMGs).”
Herschel-ATLAS: rapid evolution of dust in galaxies over the last 5 billion years (2010, background): “It is also consistent with the cold, extended dust and gas component (T = 25–30 K) of the highly lensed SMG at z = 2.3 (Swinbank et al. 2010; Danielson et al. 2011) and other lensed sources discovered by Herschel (Negrello et al. 2010).”
Dusty Star Forming Galaxies at High Redshift (2014, methodology): “Further PDR modeling using a combination of 12CO, [CI], and HCN line intensities are presented in Danielson et al. (2011).”
A survey of molecular gas in luminous sub-millimetre galaxies (2012, methodology): “It is very similar, however, to the well-studied, strongly lensed SMG SMM J2135−0102 (‘The Cosmic Eyelash’; Danielson et al. 2011), showing a similar peak and falloff towards higher Jup.”
Variations in the Galactic star formation rate and density thresholds for star formation (2012, background): “These surface- and volume-density relations potentially unify our understanding of SFRs from the nearest star forming regions to ultra-luminous infrared galaxies (ULIRGs) and even star forming regions at intermediate to high redshifts (Swinbank et al. 2010; Danielson et al. 2011).”
Rotational support of giant clumps in high-z disc galaxies (2011, background): “Indeed, the empirical values at high redshift aren(H2) ∼ 103−4 cm−3 and 30 − 80K (e.g., Danielson et al. 2011).”
MOST SUBMILLIMETER GALAXIES ARE MAJOR MERGERS (2010, background): “4, and hence be at least partially responsible for the small dynamical masses we derive for these two galaxies (see also the discussion in Danielson et al. 2010).”