Recent star formation in the inner Galactic bulge seen by ISOGAL

Abstract

We present 5-38 μm spectroscopic observations of a sample of 68 ISOGAL sources with unknown natures, taken with the Spitzer Infrared Spectrograph. Based on the characteristics and the slope of their spectra, we classified the sources as young or late-type evolved objects. These sources were selected to test selection criteria based on the ISOGAL [7]-[15] color and the spatial extent parameter σ 15 . We revised these criteria until they reliably distinguished between young and late-type evolved objects and then applied them to all ISOGAL sources in the central molecular zone (CMZ), resulting in the selection of 485 sources believed to be young. Furthermore, we added 656 Midcourse Space Experiment (MSX) sources to the CMZ sample that fulfilled F E /F D > 2 with F D and F E being the flux densities in the D (15 μm) and E (21 μm) bands. After obtaining L bol F 15 conversion factors, we calculated the bolometric luminosity, L bol , values for the CMZ sample and subsequently the masses of the sources. Applying a Kroupa initial mass function, we derived the total mass in young objects that have been formed over the last 1 Myr, resulting in an average star formation rate of 0.08 solar masses per year for the CMZ.

The Fermi Galactic Center GeV Excess and Implications for Dark Matter

“…The CMZ contains very dense molecular clouds which can host intensive star formation (e.g., Longmore et al 2013), and, as a result, a significant rate of supernovae explosions. The star formation rate (SFR) 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).…”

Multiwavelength features of Fermi bubbles as signatures of a Galactic wind

“…Mid-infrared observations by Yusuf-Zadeh et al (2009) have led to an estimate of SFR ranging between 0.007-0.14 M⊙ yr −1 , over the last 10 Gyr. Observations of young stellar objects in the central molecular zone (CMZ) in the 5-38 µm band with Spitzer allowed Immer et al (2011) to estimate a SFR of ∼ 0.08 M⊙ yr −1 . The diffuse hard Xray emission in the Galactic centre region was used by Muno et al (2004) to estimate an energy input of ∼ 10 40 erg s −1 .…”

High-energy emission from galaxies: the star-formation/gamma-ray connection

“…The supernova rate of the CMZ has been estimated by a number of different methods including the FIR-supernova rate relation, stellar composition models, and pulsar population studies (see Crocker et al 2011 for a detailed discussion). Since the distance to NGC 253 is much larger than to the centre of our Galaxy, young stellar objects are too faint to be detected by current instruments, hence the SFR has to be inferred by indirect approaches such as the scaling relation between SFR and IR flux (Kennicutt 1998). The supernova rate also has to be indirectly inferred, from e.g.…”