STAR FORMATION IN THE CENTRAL 400 PC OF THE MILKY WAY: EVIDENCE FOR A POPULATION OF MASSIVE YOUNG STELLAR OBJECTS

By F. Yusef-Zadeh, J. Hewitt, R. G. Arendt, B. Whitney, G. Rieke, M. Wardle, J. Hinz, S. Stolovy, C. Lang, M. G. Burton and 1 more. 2009

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The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gasdynamics and the formation of young stellar objects (YSOs). We probe this possibility with mid-infrared observations obtained with Infrared Array Camera and Multiband Imaging Photometer on Spitzer and with Midcourse Space Experiment. We use color–color diagrams and spectral energy distribution (SED) fits to explore the nature of YSO candidates (including objects with 4.5 μm excesses possibly due to molecular emission). There is an asymmetry in the distribution of the candidate YSOs, which tend to be found at negative Galactic longitudes; this behavior contrasts with that of the molecular gas, approximately 2/3 of which is at positive longitudes. The small-scale height of these objects suggests that they are within the Galactic center region and are dynamically young. They lie between two layers of infrared dark clouds and may have originated from these clouds. We identify new sites for this recent star formation by comparing the mid-IR, radio, submillimeter, and methanol maser data. The methanol masers appear to be associated with young, embedded YSOs characterized by 4.5 μm excesses. We use the SEDs of these sources to estimate their physical characteristics; their masses appear to range from ∼10 to ∼20 M☉. Within the central 400 × 50 pc (|l| < 1.°3 and |b| < 10′) the star formation rate (SFR) based on the identification of Stage I evolutionary phase of YSO candidates is about 0.14 M☉ yr−1. Given that the majority of the sources in the population of YSOs are classified as Stage I objects, we suggest that a recent burst of star formation took place within the last 105 yr. This suggestion is also consistent with estimates of SFRs within the last ∼107 yr showing a peak around 105 yr ago. Lastly, we find that the Schmidt–Kennicutt Law applies well in the central 400 pc of the Galaxy. This implies that star formation does not appear to be dramatically affected by the extreme physical conditions in the Galactic center region.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline (2014, background): “Most of the24µm emission (from young and evolved stars) is seen at negative longitudes where very little gas is present ( .g. Yusef-Zadeh et al. 2009).”
Variations in the Galactic star formation rate and density thresholds for star formation (2012, background): “We believe the reason our results contradict previous authors who have concluded the CMZ lies on the S-K relation (e.g. Yusef-Zadeh et al. 2009; Kennicutt & Evans 2012) is because they assumed the observed CMZ gas lay in a uniform disk and thus had a much lower average volume density.”
The Fermi Galactic Center GeV Excess and Implications for Dark Matter (2017, background): “…is rather uncertain in the CMZ and can vary from a few percent of the total SFR in the Galaxy, if traced by the free–free emission (Longmore et al. 2013), up to 10%–13%, if traced by young stellar objects (Yusef-Zadeh et al. 2009; Immer et al. 2012) or Wolf-Rayet stars (Rosslowe & Crowther 2015).”
Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, background): “The Galactic CMZ has attracted a great deal of attention recently because it has a much higher ratio of dense gas mass to star formation tracers than the rest of the galaxy (Longmore et al. 2013b, 2012, 2013a; Kruijssen et al. 2014; Yusef-Zadeh et al. 2009; Immer et al. 2012).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Evidence for variations in star formation rate on short timescales is discussed by Yusef-Zadeh et al. (2009).”
Inefficient star formation through turbulence, magnetic fields and feedback (2015, background): “The observational data are a collection of star-forming Milky Way clouds, molecular clumps and young stellar objects (YSOs) from Heiderman et al. (2010), Lada et al. (2010) and Gutermuth et al. (2011), as well as the Central Molecular Zone (CMZ) from Yusef-Zadeh et al. (2009).”
VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way (2009, background): “Nevertheless, the high mean age of the Bulge still leaves space for a small fraction of young stellar objects (YSO) which have been found in the inner Bulge (e.g., Schuller et al., 2006; Yusef-Zadeh et al., 2009).”
DEVELOPMENT OF THE MODEL OF GALACTIC INTERSTELLAR EMISSION FOR STANDARD POINT-SOURCE ANALYSIS OF FERMI LARGE AREA TELESCOPE DATA (2016, background): “It appears to be pervaded by intense magnetic fields (Morris 2014) and recently hosted a burst of star formation (Yusef-Zadeh et al. 2009).”
A 100 pc ELLIPTICAL AND TWISTED RING OF COLD AND DENSE MOLECULAR CLOUDS REVEALED BY HERSCHEL AROUND THE GALACTIC CENTER (2011, background): “The CMZ contains tens of millions of solar masses of cold interstellar matter (ISM) (Pierce-Price et al. 2000; Bally et al. 2010) and harbors several of its most active sites of star formation such as Sgr A, Sgr B2, and Sgr C (Yusef-Zadeh et al. 2008,Yusef-Zadeh et al. 2009).”
Molecular gas kinematics within the central 250 pc of the Milky Way (2016, background): “Consequently, this could favour the suggestion of Tanaka et al. (2014), that the supernovae are related to a more dispersed population of high-mass stars (there are a number of 24µm compact sources found between Sgr C and Sgr A; Yusef-Zadeh et al. 2009).”
Star formation rates and efficiencies in the Galactic Centre (2017, methodology): “In light of this, Koepferl et al. (2015) re-examined the Yusef-Zadeh et al. (2009) YSO sample, comparing in-depth radiative transfer modelling of both embedded YSOs and embedded older main sequence stars (ages of > 1 Myr).”
MAXIMALLY STAR-FORMING GALACTIC DISKS. I. STARBURST REGULATION VIA FEEDBACK-DRIVEN TURBULENCE (2011, background): “Also shown is the surface density and star formation rate in the Milky Way Galactic center, from Yusef-Zadeh et al. (2009).”
An uncertainty principle for star formation - I. Why galactic star formation relations break down below a certain spatial scale (2014, background): “…the drift of gas and young stars across the aperture boundary set the minimum scale on which galactic SF relations hold (∆xdrift ∼ 150 pc), which is consistent with the known offset between the dense gas and 24µm sources in the CMZ of the Milky Way (Yusef-Zadeh et al. 2009; Longmore et al. 2013).”
Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines (2011, background): “The CMZ is a site of recent star formation (Yusef-Zadeh et al. 2009) and very high stellar densities.”
What controls star formation in the central 500 pc of the Galaxy (2013, background): “The low observed SFR in the CMZ may therefore be spurious due to an overproduction of lowmass stars with respect to the observed massive stars, whether the SFR is determined using massive YSOs (Yusef-Zadeh et al. 2009) or the ionising flux from massive stars (Murray & Rahman 2010; Lee, Murray & Rahm”