Stellar clusters in the inner Galaxy and their correlation with cold dust emission

Stars are born within dense clumps of giant molecular clouds, constituting young stellar agglomerates known as embedded clusters, which only evolve into bound open clusters under special conditions. We statistically study all embedded clusters (ECs) and open clusters (OCs) known so far in the inner Galaxy, investigating particularly their interaction with the surrounding molecular environment and the differences in their evolution. We first compiled a merged list of 3904 clusters from optical and infrared clusters catalogs in the literature, including 75 new (mostly embedded) clusters discovered by us in the GLIMPSE survey. From this list, 695 clusters are within the Galactic range |l| < 60 deg and |b| < 1.5 deg covered by the ATLASGAL survey, which was used to search for correlations with submm dust continuum emission tracing dense molecular gas. We defined an evolutionary sequence of five morphological types: deeply embedded cluster (EC1), partially embedded cluster (EC2), emerging open cluster (OC0), OC still associated with a submm clump in the vicinity (OC1), and OC without correlation with ATLASGAL emission (OC2). Together with this process, we performed a thorough literature survey of these 695 clusters, compiling a considerable number of physical and observational properties in a catalog that is publicly available. We found that an OC defined observationally as OC0, OC1, or OC2 and confirmed as a real cluster is equivalent to the physical concept of OC (a bound exposed cluster) for ages in excess of ~16 Myr. Some observed OCs younger than this limit can actually be unbound associations. We found that our OC and EC samples are roughly complete up to ~1 kpc and ~1.8 kpc from the Sun, respectively, beyond which the completeness decays exponentially. Using available age estimates for a few ECs, we derived an upper limit of 3 Myr for the duration of the embedded phase... (Abridged)Comment: 39 pages, 9 figures. Accepted for publication in A&A on Sept 16, 2013. The catalog will be available at the CDS after official publication of the articl

Exciting Maser Science with New Instruments - the Promise of the EVLA

In the near future, the Expanded Very Large Array (EVLA) will allow surveys for maser sources with unprecedented sensitivity, spectral coverage and spectroscopic capabilities. In particular, comprehensive surveys for many maser species with simultaneous sensitive continuum imaging and absorption studies will give a comprehensive radio picture of star formation in the Galactic plane and elsewhere. Very efficient EVLA surveys for H2O megamasers in Active Galacic Nuclei will be possible to practically arbitrary redshifts. EVLA and Atacama Large Millimeter Array (ALMA) studies of H2O and SiO masers will serve as high resolution probes of the innermost envelopes of oxygen-rich evolved stars and HCN masers of carbon-rich stars. Farther in the future, the Square Kilometer Array (SKA) promises the detection of OH gigamasers at all conceivable redshifts and maser astrometry with unprecedented accuracy.Comment: 10 pages, incl. 4 figures, iaus.cls, to appear the Procedings of IAU Symp. 242 (Astrophysical masers and their environments) eds. J. Chapman & W. Baan Replaced version with a few typos correcte

Molecular Cloud-scale Star Formation in NGC 300

We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 HII regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J=2-1) observations with the APEX telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ~10^5 Msun to 7x10^5 Msun. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine GALEX FUV, Spitzer 24 micron, and H-alpha narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our HII region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way Giant Molecular Clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kpc-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.Comment: 42 pages, 14 figures, 7 tables. Includes a complete image atlas of our HII region targets. ASCII versions of tables will be available electronically after paper is published. Accepted for publication in the Astrophysical Journa

High-angular resolution observations of methanol in the infrared dark cloud core G11.11-0.12P1

Recent studies suggest that infrared dark clouds (IRDCs) have the potential of harboring the earliest stages of massive star formation and indeed evidence for this is found toward distinct regions within them. We present a study with the Plateau de Bure Interferometer of a core in the archetypal filamentary IRDC G11.11-0.12 at few arcsecond resolution to determine its physical and chemical structure. The data consist of continuum and line observations covering the C34S 2-1 line and the methanol 2_k-1_k v_t=0 lines at 3mm and the methanol 5_k-4_k v_t =0 lines at 1mm. Our observations show extended emission in the continuum at 1 and 3 mm. The methanol 2_k-1_k v_t=0 emission presents three maxima extending over 1 pc scale (when merged with single-dish short-spacing observations); one of the maxima is spatially coincident with the continuum emission. The fitting results show enhanced methanol fractional abundance (~3x10^-8) at the central peak with respect to the other two peaks, where it decreases by about an order of magnitude (~4-6x10^-9). Evidence of extended 4.5 microns emission, "wings" in the CH3OH 2_k-1_k spectra, and CH3OH abundance enhancement point to the presence of an outflow in the East-West direction. In addition, we find a gradient of ~4 km/s in the same direction, which we interpret as being produced by an outflow(s)-cloud interaction.Comment: Accepted for publication to A&