Abstract

Dust production in M31 and M33

Thavisha Dharmawardena (ASIAA)

Ciska Kemper (ASIAA), Sundar Srinivasan (ASIAA), Peter Scicluna (ASIAA), Sofia Wallström (ASIAA)

Evolved stars, in particular Asymptotic Giant Branch (AGB) stars and Red Supergiants (RSG), play a crucial role in the life cycle of dust in galaxies, as the main contributors of dust to the interstellar medium (ISM). However, present-day dust production rates (DPRs) for AGB stars and RSGs, determined using mid-infrared thermal dust emission, are insufficient to build up the observed interstellar dust reservoir and compensate for destruction by supernova shocks and astration, as is established for both the Large Magellanic Cloud (LMC; e.g. Kemper 2015) and Small Magellanic Cloud (SMC; Srinivasan et al. 2016). These conclusions are supported by calculations of the theoretical dust yield of evolved stars (Schneider et al. 2014). Although the integrated DPR over the history of the LMC and SMC appears to coincide with the interstellar dust masses derived using Herschel maps (Gordon et al. 2014), and the situation gets worse when dust destruction (Temim et al. 2015) and dust consumption by star formation (Skibba et al. 2012) are taken into account.

The DPRs for the LMC and SMC were determined from the SAGE and SAGE-SMC Spitzer imaging surveys, using all four IRAC bands and MIPS 24μm photometry of AGB stars and RSGs, complemented with near-infrared and optical data. Individual DPRs were determined by fitting these photometry with the GRAMS dust radiative transfer models (Srinivasan et al. 2011; Sargent et al. 2011), and integrated over the entire galaxy to produce the total DPR. At 50 and 60 kpc, the LMC and SMC are close enough to unambiguously resolve the evolved stellar population using Spitzer, down to the tip of the Red Giant Branch (RGB), and include the entire AGB/RSG population. However, Spitzer studies of the more distant M32 (Jones et al. 2015) and M33 (Javadi et al. 2013) are limited to the brightest AGB stars and RSGs in the infrared -- which fortunately happen to be the most dusty objects -- and suffer from confusion due to the large PSF of Spitzer. To determine the DPRs for M32 and M33, these teams were confined to the IRAC data, introducing great uncertainty on the DPR; mid-infrared photometry would mitigate this issue.

JWST will facilitate studies of integrated DPRs for more distant galaxies. The high sensitivity of the JWST’s MIRI and NIRCAM instruments will allow observations to reach the tip of the RGB and include the entire AGB and RSG sample throughout the Local Group. Furthermore, the smaller PSF reduces the confusion issues that hampered Spitzer studies of more distant Local Group galaxies, enabling mid-infrared photometric measurements. We propose a sampling imaging survey of galaxies M31 and M33, at 752 kpc (Riess et al. 2012) and 820 kpc (Conn et al. 2012) the nearest spiral galaxies, and Milky Way analogs, in our Local Group. We will use MIRI and NIRCAM to target a number of representative fields. Based on the population of evolved stars in the LMC, we estimate that there may be up to 400 AGB stars and RSGs in each MIRI pointing, with a range of DPRs. The GRAMS model grid will be applied to determine individual DPRs, and, with a set of well-chosen fields, we can extrapolate these values to determine the overall DPR for both galaxies using the stellar distributions.

The global DPRs for M31 and M33 will be compared with the interstellar dust masses measured in the infrared, and parameters such as the star formation rate and dust destruction rate by shocks to evaluate the dust budget in these nearby Milky Way analogs. Moreover, this will extend the study of dust production to high-metallicity galaxies for the first time, revealing the importance of cosmic enrichment in dust production.

Mode of presentation: poster