SPITZERSAGE SURVEY OF THE LARGE MAGELLANIC CLOUD. III. STAR FORMATION AND ∼1000 NEW CANDIDATE YOUNG STELLAR OBJECTS

Abstract

We present ∼1000 new candidate Young Stellar Objects (YSOs) in the Large Magellanic Cloud selected from Spitzer Space Telescope data, as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) Legacy program. The YSOs, detected by their excess infrared (IR) emission, represent early stages of evolution, still surrounded by disks and/or infalling envelopes. Previously, fewer than 20 such YSOs were known. The candidate YSOs were selected from the SAGE Point Source Catalog from regions of color-magnitude space least confused with other IR-bright populations. The YSOs are biased toward intermediate-to high-mass and young evolutionary stages, because these overlap less with galaxies and evolved stars in color-magnitude space. The YSOs are highly correlated spatially with atomic and molecular gas, and are preferentially located in the shells and bubbles created by massive stars inside. They are more clustered than generic point sources, as expected if star formation occurs in filamentary clouds or shells. We applied a more stringent color-magnitude selection to produce a subset of "high-probability" YSO candidates. We fitted the spectral-energy distributions (SEDs) of this subset and derived physical properties for those that were well fitted. The total mass of these well-fitted YSOs is ∼2900 M and the total luminosity is ∼2.1 × 10 6 L . By extrapolating the mass function with a standard initial mass function and integrating, we calculate a current star-formation rate of ∼0.06 M yr −1 , which is at the low end of estimates based on total ultraviolet and IR flux from the galaxy (∼0.05 − 0.25 M yr −1 ), consistent with the expectation that our current YSO list is incomplete. Follow-up spectroscopy and further data mining will better separate the different IR-bright populations and likely increase the estimated number of YSOs. The full YSO list is available as electronic tables, and the SEDs are available as an electronic figure for further use by the scientific community.

The impact of stellar feedback on the density and velocity structure of the interstellar medium

“…Our MW-like simulation with feedback features a SFR of ∼ 4 M yr −1 at t = 450 Myr, which is a factor of a few greater than observed (Licquia & Newman 2015, found ∼ 1.65 M yr −1 for the Milky Way). In the LMC-like simulation with feedback we find a SFR ∼ 0.1 − 0.2 M yr −1 at t = 450 Myr, which is a close match to values derived from observations of the LMC, ∼ 0.14 M yr −1 (Murray & Rahman 2010) and ∼ 0.25 M yr −1 (Whitney et al 2008), thus showing that despite the differences between our simulations and observations, at late times (t 200) our MW-like and LMC-like simulations with feedback produce global star formation rates that are compatible with those measured from observations. For our SMC feedback simulation we find a SFR ∼ 0.3 − 0.4 M yr −1 at t = 450 Myr.…”

“…SFRs than the LMC-like simulations, whereas the opposite is found in observations (see Kennicutt & Hodge 1986;Wilke et al 2004;Whitney et al 2008). The origin of this discrepancy is the adopted initial conditions.…”

Star Formation in the Central 400 Pc of the Milky Way: Evidence for a Population of Massive Young Stellar Objects

“…The left side of the slope in Figure 7(a) indicates a trend of IR excess sources with luminosity. The CMD of the Large Magellanic Cloud (LMC) shows a similar trend which is due to a linear relationship between more luminous AGB stars with increasing radiation pressure, and more mass loss of the dust, and therefore more IR excess (see Figure 3(a) of Whitney et al 2008). Thus, we believe the sources to the right of the slope in Figure 7( Figure 7(b) where the candidate YSOs are shown as crosses.…”

The Data Big Bang and the Expanding Digital Universe: High‐Dimensional, Complex and Massive Data Sets in an Inflationary Epoch

“…Simple color-magnitude diagrams are another traditional tool taking advantage of multiple data dimensions (e.g., cataloging YSO candidates from Spitzer survey data, Whitney et al [37]). In addition, it is well known that simple color-color plots using four colors provide ways to efficiently and fairly reliably classify into physical types a large number of objects (IRAS data, e.g., [38,39]; 2MASS data, e.g., [40] MSX data, e.g., [41,42]; Spitzer data, e.g., [43]) as well as to discover interesting new objects as outliers (e.g., Luminous Red Novae, [44,45]).…”

“…When spectra are considered and compared in detail, the huge number of emission and absorption features obviously compounds the problem vastly. Still more complexity is added when one attempts to correlate a large grid of models with a large data set having many dimensions (e.g., the YSO analysis [37]) in order to create feedback for models based on statistically significant samples rather than on a few putative prototypes.…”