Heracles: The Hera Co Line Extragalactic Survey

Abstract

We present the HERA CO-Line Extragalactic Survey (HERACLES), an atlas of CO emission from 18 nearby galaxies that are also part of The H I Nearby Galaxy Survey (THINGS) and the Spitzer Infrared Nearby Galaxies Survey (SINGS). We used the HERA multi-pixel receiver on the IRAM 30-m telescope to map the CO J = 2 → 1 line over the full optical disk (defined by the isophotal radius r 25 ) of each target, at 13 ′′ angular resolution and 2.6 km s −1 velocity resolution. Here we describe the observations and reduction of the data and show channel maps, azimuthally averaged profiles, integrated intensity maps, and peak intensity maps. The implied H 2 masses range from 7 × 10 6 to 6 × 10 9 M ⊙ , with four low metallicity dwarf irregular galaxies yielding only upper limits. In the cases where CO is detected, the integrated H 2 -to-H I ratios range from 0.02 -1.13 and H 2 -to-stellar mass ratios from 0.01 to 0.25. Exponential scale lengths of the CO emission for our targets are in the range 0.8 -3.2 kpc, or 0.2 ± 0.05 r 25 . The intensity-weighted mean velocity of CO matches that of H I very well, with a 1σ scatter of only 6 km s −1 . The CO J = 2 → 1/J = 1 → 0 line ratio varies over a range similar to that found in the Milky Way and other nearby galaxies, ∼ 0.6-1.0, with higher values found in the centers of galaxies. The typical line ratio, ∼ 0.8, could be produced by optically thick gas with an excitation temperature of ∼ 10 K.

What powers the starburst activity of NGC 1068? Star-driven gravitational instabilities caught in the act

“…2 shows that Σco(R) is depressed at small radii relative to an exponential radial distribution, as was also pointed out by Regan et al (2001) and Helfer et al (2003). Exponential distributions are traditionally used for fitting the radial profiles of CO surface brightness observed in nearby galaxies, and thus for inferring important physical parameters such as the scale length of the molecular disc and, when relevant, its central surface density (e.g., Young & Scoville 1982;Young et al 1995;Sakamoto et al 1999;Regan et al 2001;Helfer et al 2003;Leroy et al 2008Leroy et al , 2009). Fig.…”

Dusty star-forming galaxies at high redshift

“…Utilizing data from the THINGS, HERACLES, and BIMA SONG surveys Leroy et al, 2009;Helfer et al, 2003), Bigiel et al (2008) investigated the resolved star formation law in nearby galaxies. These authors found that the SFR is principally correlated with H 2 gas (as traced by CO (J=2-1) in this case), and unassociated with HI in nearby galaxies.…”

Galaxy pairs in the SDSS – XIII. The connection between enhanced star formation and molecular gas properties in galaxy mergers

“…The most common approach to deal with this issue is to apply an aperture correction to the CO flux measurements. This is frequently done by utilising resolved CO maps of similar sources (Regan et al 2001;Kuno et al 2007;Leroy et al 2009) to estimate the amount of missed flux (Bothwell et al 2013;Saintonge et al 2011a), assuming a smooth gas profile which follows the distribution of stellar light. However, studies based on both isothermal simulations and spatially resolved maps show that during a galaxy encounter the distribution of molecular gas is less uniform, with CO emission located along tidal features, dust lanes or in extended disks (Shlosman et al 1989;Konig et al 2014;Ueda et al 2014 Kauffmann et al (2003) classification, by using the SFR-D4000 relation (Brinchmann et al 2004).…”