TY - JOUR
T1 - Alma reveals the molecular medium fueling the nearest nuclear starburst
AU - Leroy, Adam K.
AU - Bolatto, Alberto D.
AU - Ostriker, Eve Charis
AU - Rosolowsky, Erik
AU - Walter, Fabian
AU - Warren, Steven R.
AU - Meyer, Jennifer Donovan
AU - Hodge, Jacqueline
AU - Meier, David S.
AU - Ott, Jürgen
AU - Sandstrom, Karin
AU - Schruba, Andreas
AU - Veilleux, Sylvain
AU - Zwaan, Martin
N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved..
PY - 2015/3/1
Y1 - 2015/3/1
N2 - We use ALMA observations to derive mass, length, and time scales associated with NGC 253's nuclear starburst. This region forms 2 M⊙ yr-1 of stars and resembles other starbursts in ratios of gas, dense gas, and star formation tracers, with star formation consuming the gas reservoir at a normalized rate 10 times higher than in normal galaxy disks. We present new 35 pc resolution observations of bulk gas tracers (CO), high critical density transitions (HCN, HCO+, and CS), and their isotopologues. The starburst is fueled by a highly inclined distribution of dense gas with vertical extent <100 pc and radius 250 pc. Within this region, we identify 10 starburst giant molecular clouds (GMCs) that appear as both peaks in the dense gas tracer cubes and the HCN-to-CO ratio map. These are massive (107 M⊙) structures with sizes (30 pc) similar to GMCs in other systems, but compared to GMCs in normal galaxy disks, they have high line widths (σ 20-40 km s-1, Mach number ) and high surface and volume densities (Σmol 6000 M⊙ pc-2, n H2 2000 cm-3). The self gravity from such high densities can explain the high line widths and the short free fall time τff 0.7 Myr in the clouds helps explain the more efficient star formation in NGC 253. Though the high inclination obscures the geometry somewhat, we show that simple models suggest a compact, clumpy region of high gas density embedded in a more extended, non-axisymmetric, bar-like distribution. Over the starburst, the surface density still exceeds that of a typical disk galaxy GMC and, as in the clouds, timescales in the disk as a whole are short compared to those in normal galaxy disks. The orbital time (10 Myr), disk free fall time (≲ 3 Myr), and disk crossing time (≲ 3 Myr) are each an order of magnitude shorter than in a normal galaxy disk. Finally, the CO-to-H2 conversion factor implied by our cloud calculations is approximately Galactic, contrasting with results showing a low value for the whole starburst region. The contrast provides resolved support for the idea of mixed molecular ISM phases in starburst galaxies.
AB - We use ALMA observations to derive mass, length, and time scales associated with NGC 253's nuclear starburst. This region forms 2 M⊙ yr-1 of stars and resembles other starbursts in ratios of gas, dense gas, and star formation tracers, with star formation consuming the gas reservoir at a normalized rate 10 times higher than in normal galaxy disks. We present new 35 pc resolution observations of bulk gas tracers (CO), high critical density transitions (HCN, HCO+, and CS), and their isotopologues. The starburst is fueled by a highly inclined distribution of dense gas with vertical extent <100 pc and radius 250 pc. Within this region, we identify 10 starburst giant molecular clouds (GMCs) that appear as both peaks in the dense gas tracer cubes and the HCN-to-CO ratio map. These are massive (107 M⊙) structures with sizes (30 pc) similar to GMCs in other systems, but compared to GMCs in normal galaxy disks, they have high line widths (σ 20-40 km s-1, Mach number ) and high surface and volume densities (Σmol 6000 M⊙ pc-2, n H2 2000 cm-3). The self gravity from such high densities can explain the high line widths and the short free fall time τff 0.7 Myr in the clouds helps explain the more efficient star formation in NGC 253. Though the high inclination obscures the geometry somewhat, we show that simple models suggest a compact, clumpy region of high gas density embedded in a more extended, non-axisymmetric, bar-like distribution. Over the starburst, the surface density still exceeds that of a typical disk galaxy GMC and, as in the clouds, timescales in the disk as a whole are short compared to those in normal galaxy disks. The orbital time (10 Myr), disk free fall time (≲ 3 Myr), and disk crossing time (≲ 3 Myr) are each an order of magnitude shorter than in a normal galaxy disk. Finally, the CO-to-H2 conversion factor implied by our cloud calculations is approximately Galactic, contrasting with results showing a low value for the whole starburst region. The contrast provides resolved support for the idea of mixed molecular ISM phases in starburst galaxies.
KW - ISM: molecules
KW - galaxies: ISM
KW - galaxies: star formation
KW - galaxies: starburst
KW - radio lines: ISM
KW - radio lines: galaxies
KW - stars: formation
UR - http://www.scopus.com/inward/record.url?scp=84924284407&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84924284407&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/801/1/25
DO - 10.1088/0004-637X/801/1/25
M3 - Article
AN - SCOPUS:84924284407
SN - 0004-637X
VL - 801
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 25
ER -