17 research outputs found
The UK Infrared Telescope M33 monitoring project. III. Feedback from dusty stellar winds in the central square kiloparsec
We have conducted a near-infrared monitoring campaign at the UK InfraRed
Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main
aim was to identify stars in the very final stage of their evolution, and for
which the luminosity is more directly related to the birth mass than the more
numerous less-evolved giant stars that continue to increase in luminosity. In
this third paper of the series, we measure the dust production and rates of
mass loss by the pulsating Asymptotic Giant Branch (AGB) stars and red
supergiants. To this aim, we combined our time-averaged near-IR photometry with
the multi-epoch mid-IR photometry obtained with the Spitzer Space Telescope.
The mass-loss rates are seen to increase with increasing strength of pulsation
and with increasing bolometric luminosity. Low-mass stars lose most of their
mass through stellar winds, but even super-AGB stars and red supergiants lose
% of their mass via a dusty stellar wind. More than three-quarters of
the dust return is oxygenous. We construct a 2-D map of the mass-return rate,
showing a radial decline but also local enhancements due to agglomerations of
massive stars. We estimate a total mass-loss rate of 0.004--0.005 M
yr kpc, increasing to M yr kpc
when accounting for eruptive mass loss (e.g., supernov{\ae}); comparing this to
the current star formation rate of M yr kpc we
conclude that star formation in the central region of M\,33 can only be
sustained if gas is accreted from further out in the disc or from
circum-galactic regions.Comment: Accepted for publication in MNRA
The UK Infrared Telescope M33 monitoring project. II. The star formation history in the central square kiloparsec
We have conducted a near-infrared monitoring campaign at the UK InfraRed
Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main
aim was to identify stars in the very final stage of their evolution, and for
which the luminosity is more directly related to the birth mass than the more
numerous less-evolved giant stars that continue to increase in luminosity. In
this second paper of the series, we construct the birth mass function and hence
derive the star formation history. The star formation rate has varied between
~0.002 and 0.007 M yr^-1 kpc^-2. We give evidence of two epochs of a
star formation rate enhanced by a factor of a few -- one that happened \geq 6
Gyr ago and produced \geq 80% of the total mass in stars, and one around 250
Myr ago that lasted ~ 200 Myr and formed \leq 6% of the mass in stars. We
construct radial and azimuthal distributions in the image plane and in the
galaxy plane for populations associated with old first-ascent red giant branch
(RGB) stars, intermediate-age Asymptotic Giant Branch (AGB) stars and young
(massive) blue and red supergiants. We find that the RGB stars follow a
spheroidal distribution, while younger stars follow a flat-disc distribution.
The intermediate-age population displays signs of a pseudo-bulge or possibly a
bar. The inner spiral arm pattern as recorded in mid-19^th-century drawings is
confirmed. We interpret our findings as evidence for an old, pressure-supported
component and a younger disc formed 6 Gyr ago, with an accretion event
occurring 250 Myr ago giving rise to the compact nucleus in M33. Our study
provides support for recent Padova stellar evolution models except that
super-AGB stars likely reach low temperatures and thus high mass-loss rates,
supporting the super-AGB nature of the progenitors of dust-enshrouded
supernovae such as SN2008S.Comment: Accepted for publication in MNRA
The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. VI. The Star Formation History and Dust Production in Andromeda IX
We present a photometric study of the resolved stellar populations in Andromeda IX (And IX), the closest satellite to M31, a metal-poor and low-mass dwarf spheroidal galaxy. We estimate a distance modulus of mag based on the tip of the red giant branch. By probing the variability of asymptotic giant branch stars, we study the star formation history of And IX. We identified 50 long-period variables (LPVs) in And IX using the Isaac Newton Telescope in two filters, the Sloan and Harris . In this study, we selected LPVs within two half-light radii with amplitudes in the range of 0.2β2.20 mag. It is found that the peak of star formation reaches at β6 Gyr ago. Our findings suggest an outside-in galaxy formation scenario for And IX with a quenching occurring Gyr ago with a star formation rate (SFR) in the order of at redshift <0.5. We calculate the total stellar mass by integrating the SFR within two half-light radii . By employing spectral energy distribution fitting for the observed LPVs in And IX, we evaluate a mass-loss rate in the range of . Finally, we show that the total mass deposition to the interstellar medium (ISM) is from the C- and O-rich types of dust-enshrouded LPVs. The ratio of the total mass returned to the ISM by LPVs to the total stellar mass is , and so at this rate it would take βΌ1 Gyr to reproduce this galaxy