Aims. The Herschel survey of the Galactic plane (Hi-GAL) provides a unique opportunity to study star formation over large areas of the sky and different environments in the Milky Way. We use the best-studied Hi-GAL fields to date, two 2 • · 2 • tiles centered on ( , b) = (30 • , 0 • ) and ( , b) = (59 • , 0 • ), to study the star formation activity in these regions of the sky using a large sample of well-selected young stellar objects (YSOs). Methods. We used the science demonstration phase Hi-GAL fields, where a tremendous effort has been made to identify the newly formed stars and to derive their properties as accurately as possible, e.g. distance, bolometric luminosity, envelope mass, and stage of evolution. We estimated the star formation rate (SFR) for these fields using the number of candidate YSOs and their average time scale to reach the zero age main sequence, and compared it with the rate estimated using their integrated luminosity at 70 μm, combined with an extragalactic star formation indicator. Results. We measure an SFR of (9.5 ± 4.3) × 10 −4 M /yr and (1.6 ± 0.7) × 10 −4 M /yr with the source counting method, in = 30 • and = 59 • , respectively. Results with the 70 μm estimator are (2.4 ± 0.4) × 10 −4 M /yr and (2.6 ± 1.1) × 10 −6 M /yr. Since the 70 μm indicator is derived from averaging extragalactic star forming complexes, we extrapolated of these values to the whole Milky Way and obtain SFR MW = (0.71 ± 0.13) M /yr from l = 30 • and SFR MW = (0.10 ± 0.04) M /yr from = 59 • . The estimates in = 30 • agree with the most recent results for Galactic star formation activity. Conclusions. The source-counting method gives results that are only valid for the particular region under consideration. In contrast, the construction of the IR indicator leads to results that can be extrapolated to the whole Galaxy. In particular, when it is applied to the = 30 • field, it provides an SFR that is consistent with previous estimates, indicating that the characteristics of this field are very likely close to those of the star formation-dominated galaxies used for its derivation. Since the sky coverage is limited, this analysis will improve when the full Hi-GAL survey is available. It will cover the whole Galactic plane, sampling almost the totality of Galactic star forming complexes. By means of the candidate YSO-counting method, it will then be possible to calibrate an SFR Galactic indicator and to test the validity of the extragalactic estimators.

We present wide‐area radio continuum 5.5 and 8.8 GHz (5.5 and 3.4 cm) Australia Telescope Compact Array observations of the complex and rich massive star‐forming region G305. The aim of this study is to perform an un‐targeted survey of the region in search of the compact radio emission associated with ultracompact (UC) H ii regions. Observations presented here encompass the entire complex and have a maximum resolution of ∼ 1.5 × 1.4  arcsec and sensitivity of ∼0.07 mJy beam−1. By applying a data reduction method that emphasizes small‐scale structure, we are able to detect 71 compact radio sources distributed throughout the observed field. To explore the nature of these compact radio sources we compare to mid‐infrared data and in this way identify 56 background sources, eight stellar radio sources, a single bright‐rimmed cloud and six candidate UC H ii regions. The physical properties of these candidate UC H ii regions are determined and reveal that five candidates have peak properties consistent with known UC H ii regions with source radii ranging from 0.04 to 0.1 pc, emission measures from 2.56 to 10.3 × 10−6 pc cm−6 and electron densities of 0.34–1.03 × 104 cm−3. We comment on these sites of recent massive star formation within G305 and by comparing to other star formation tracers (masers, NH3 and young stellar objects) build a picture of the star formation history of the region. Using these results we estimate a lower limit to the star formation rate for the region of ∼0.003 M⊙ yr−1.

We present a Herschel far‐infrared study towards the rich massive star‐forming complex G305, utilizing PACS 70, 160 μm and SPIRE 250, 350, and 500 μm observations from the Hi‐GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star‐forming population within G305, by combining far‐infrared data with radio continuum, H2O maser, methanol maser, MIPS and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multiwavelength data set, which can then be identified from the derived properties obtained from fitted spectral energy distributions (SEDs). By SED modelling using both a simple modified blackbody and fitting to a comprehensive grid of model SEDs, some 16 candidate associations are identified as embedded massive star‐forming regions. We derive a two‐selection colour criterion from this sample of log (F70/F500) ≥ 1 and log (F160/F350) ≥ 1.6 to identify an additional 31 embedded massive star candidates with no associated star formation tracers. Using this result we can build a picture of the present‐day star formation of the complex, and by extrapolating an initial mass function, suggest a current population of ≈2 × 104 young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01–0.02 M⊙ yr−1. Comparing this resolved SFR, to extragalactic SFR tracers (based on the Kennicutt–Schmidt relation), we find that the star formation activity is underestimated by a factor of ≥2 in comparison to the SFR derived from the YSO population.

We present 109-115 GHz (3 mm) wide-field spectral line observations of 12 CO, 13 CO and C 18 O J = 1-0 molecular emission and 5.5 and 8.8 GHz (6 and 3 cm) radio continuum emission towards the high-mass star forming complex known as G305. The morphology of G305 is dominated by a large evacuated cavity at the centre of the complex driven by clusters of O stars surrounded by molecular gas. Our goals are to determine the physical properties of the molecular environment and reveal the relationship between the molecular and ionised gas and star formation in G305. This is in an effort to characterise the star-forming environment and constrain the star formation history in an attempt to evaluate the impact of high-mass stars on the evolution of the G305 complex.Analysis of CO emission in G305 reveals 156 molecular clumps with the following physical characteristics; excitation temperatures ranging from 7-25 K, optical depths of 0.2-0.9, H 2 column densities of 0.1-4.0 × 10 22 cm −2 , clump masses ranging from 10 2 -10 4 M and a total molecular mass of > 3.5 × 10 5 M . The 5.5 and 8.8 GHz radio continuum emission reveals an extended low surface brightness ionised environment within which we identify 15 large-scale features with a further eight smaller sources projected within these features. By comparing to mid infrared emission and archival data, we identify nine HII regions, seven compact HII regions, one UCHII region, four extended regions. The total integrated flux of the radio continuum emission at 5.5 GHz is ∼ 180 Jy corresponding to a Lyman continuum output of 2.4 × 10 50 photons s −1 . We compare the ionised and molecular environment with optically identified high-mass stars and ongoing star formation, identified from the literature. Analysis of this dataset reveals a star formation rate of 0.008-0.016 M yr −1 and efficiency of 7-12%, allows us to probe the star formation history of the region and discuss the impact of high-mass stars on the evolution of G305.

No abstract