The conversion of gas into stars is a fundamental process in astrophysics and cosmology. Stars are known to form from the gravitational collapse of dense clumps in interstellar molecular clouds, and it has been proposed that the resulting star formation rate is proportional to either the amount of mass above a threshold gas surface density, or the gas volume density. These star-formation prescriptions appear to hold in nearby molecular clouds in our Milky Way Galaxy's disk as well as in distant galaxies where the star formation rates are often much larger. The inner 500 pc of our Galaxy, the Central Molecular Zone (CMZ), contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of star-formation prescriptions can be tested. Here we show that by several measures, the current star formation rate in the CMZ is an order-ofmagnitude lower than the rates predicted by the currently accepted prescriptions. In particular, the region 1 • < l < 3.5 • , |b| < 0.5 • contains ∼ 10 7 M ⊙ of dense molecular gas -enough to form 1000 Orion-like clusters -but the present-day star formation rate within this gas is only equivalent to that in Orion. In addition to density, another property of molecular clouds, such as the amplitude of turbulent motions, must be included in the star-formation prescription to predict the star formation rate in a given mass of molecular gas.The rate at which gas is converted into stars has been measured in the disks of nearby galaxies. When averaged over hundreds of parsecs, the star-formation rate (SFR) was found to have a power-law dependence on the gas surface-density as described by the Schmidt-Kennicutt (SK) relations (Schmidt 1959;Kennicutt 1998;Kennicutt & Evans 2012). A linear relationship is found between SFR and gas surface-density above a local extinction threshold, AK ∼0.8 magnitudes at a near-infrared wavelength of 2.2 µm, corresponding to a gas column-density of ∼ 7.4 × 10 21

The under-abundance of very massive galaxies 1,2 in the universe is frequently attributed to the effect of galactic winds 3,4,5,6 . Although ionized galactic winds are readily observable most of the expelled mass is likely in cooler atomic 7,8 and molecular phases 9,10,11 . Expanding molecular shells observed in starburst systems such as NGC 253 12 and M 82 13,14 may facilitate the entrainment of molecular gas in the wind. While shell properties are well constrained 12 , determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution <100 pc coupled with sensitivity to a wide range of spatial scales, hitherto not available. Here we report observations of NGC 253, a nearby 15 starburst galaxy (D~3.4 Mpc) known to possess a wind 16,17,18,19,20 , which trace the cool molecular wind at 50 pc resolution. At this resolution the extraplanar

Context. The Galactic center is the closest region where we can study star formation under extreme physical conditions like those in high-redshift galaxies. Aims. We measure the temperature of the dense gas in the central molecular zone (CMZ) and examine what drives it. Methods. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3-2 para-formaldehyde (p-H 2 CO) transitions. We used the 3 2,1 −2 2,0 / 3 0,3 −2 0,2 line ratio to determine the gas temperature in n ∼ 10 4 −10 5 cm −3 gas. We have produced temperature maps and cubes with 30 and 1 km s −1 resolution and published all data in FITS form. Results. Dense gas temperatures in the Galactic center range from ∼60 K to >100 K in selected regions. The highest gas temperatures T G > 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km s −1 and 50 km s −1 clouds, and in "The Brick" (G0.253+0.016). We infer an upper limit on the cosmic ray ionization rate ζ CR < 10 −14 s −1 . Conclusions. The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies, in particular starburst systems. The gas temperature is uniformly higher than the dust temperature, confirming that dust is a coolant in the dense gas. Turbulent heating can readily explain the observed temperatures given the observed line widths. Cosmic rays cannot explain the observed variation in gas temperatures, so CMZ dense gas temperatures are not dominated by cosmic ray heating. The gas temperatures previously observed to be high in the inner ∼75 pc are confirmed to be high in the entire CMZ.

We use new ALMA observations to derive the mass, length, and time scales associated with the disk and the star-forming clouds in the starburst at the heart of the nearby spiral galaxy NGC 253. This region forms ∼ 2 M yr −1 of stars and resembles other starburst systems in star formation-CO-HCN scaling relations, with star formation consuming the gas reservoir at a normalized rate 10 times higher than in normal galaxy disks. We present sensitive ∼ 35 pc resolution observations of the bulk gas tracers CO and C 17 O and the high critical density transitions HCN (1-0), HCO + (1-0), and CS (2-1) 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 ten starburst giant molecular clouds that appear as both peaks in the dense gas tracer cubes and enhancements in the HCN-to-CO ratio map. These clouds appear as massive (∼ 10 7 M ) structures with sizes (∼ 30 pc) similar to GMCs in other systems, but when compared to a large literature compilation they show very high line widths (σ ∼ 20-40 km s −1 ) given their size, with implied Mach numbers as high as M ∼ 90. The clouds also show very high surface densities (∼ 6, 000 M pc −2 ) and volume densities (n H2 ∼ 2, 000 cm −3 ). The self gravity from such high densities is sufficient to explain the high line widths and the short free fall time τ ff ∼ 0.7 Myr in the clouds may explain the more efficient star formation in NGC 253. We also consider the starburst region as a whole. The geometry is confused by the high inclination, but we show that simple models support a non-axisymmetric, bar-like geometry with a compact, clumpy region of high gas density embedded in an extended CO distribution. Even when considering the region as a whole, the surface density still vastly exceeds that of a typical disk galaxy GMC. 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 spiral galaxy disk. We compare to simple models with mixed success, showing that some but not all aspects of the structure correspond to the predictions from assuming vertical dynamical equilibrium or a marginally stable thin gas disk. Finally, the CO-to-H 2 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.

Context. Amino acids are building blocks of proteins and therefore key ingredients for the origin of life. The simplest amino acid, glycine (NH 2 CH 2 COOH), has long been searched for in the interstellar medium but has not been unambiguously detected so far. At the same time, more and more complex molecules have been newly found toward the prolific Galactic center source Sagittarius B2. Aims. Since the search for glycine has turned out to be extremely difficult, we aimed at detecting a chemically related species (possibly a direct precursor), amino acetonitrile (NH 2 CH 2 CN). Methods. With the IRAM 30 m telescope we carried out a complete line survey of the hot core regions Sgr B2(N) and (M) in the 3 mm range, plus partial surveys at 2 and 1.3 mm. We analyzed our 30 m line survey in the LTE approximation and modeled the emission of all known molecules simultaneously. We identified spectral features at the frequencies predicted for amino acetonitrile lines having intensities compatible with a unique rotation temperature. We also used the Very Large Array to look for cold, extended emission from amino acetonitrile. Results. We detected amino acetonitrile in Sgr B2(N) in our 30 m telescope line survey and conducted confirmatory observations of selected lines with the IRAM Plateau de Bure and the Australia Telescope Compact Array interferometers. The emission arises from a known hot core, the Large Molecule Heimat, and is compact with a source diameter of 2 (0.08 pc). We derived a column density of 2.8 × 10 16 cm −2 , a temperature of 100 K, and a linewidth of 7 km s −1 . Based on the simultaneously observed continuum emission, we calculated a density of 1.7 × 10 8 cm −3 , a mass of 2340 M , and an amino acetonitrile fractional abundance of 2.2 × 10 −9 . The high abundance and temperature may indicate that amino acetonitrile is formed by grain surface chemistry. We did not detect any hot, compact amino acetonitrile emission toward Sgr B2(M) or any cold, extended emission toward Sgr B2, with column-density upper limits of 6 × 10 15 and 3 × 10 12−14 cm −2 , respectively. Conclusions. Based on our amino acetonitrile detection toward Sgr B2(N) and a comparison to the pair methylcyanide/acetic acid both detected in this source, we suggest that the column density of both glycine conformers in Sgr B2(N) is well below the best upper limits published recently by other authors, and probably below the confusion limit in the 1−3 mm range.