- ID:
- ivo://CDS.VizieR/J/ApJ/789/147
- Title:
- Star formation histories of LG dwarf galaxies
- Short Name:
- J/ApJ/789/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with {tau} ~ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH ({tau} ~ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10^5^ M_{sun}_ to 30% for galaxies with M > 10^7^ M_{sun}_) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.
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- ID:
- ivo://CDS.VizieR/J/AJ/127/1531
- Title:
- Star formation history of SMC
- Short Name:
- J/AJ/127/1531
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4{deg}x4.5{deg} area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/661/L143
- Title:
- Star formation rate in Seyfert galaxies
- Short Name:
- J/ApJ/661/L143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Feedback from black hole activity is widely believed to play a key role in regulating star formation and black hole growth. A long-standing issue is the relation between star formation and the fueling of the supermassive black holes in active galactic nuclei (AGNs). We compile a sample of 57 Seyfert galaxies to tackle this issue. We estimate the surface densities of gas and star formation rates in circumnuclear regions (CNRs). Comparing them with the well-known Kennicutt-Schmidt (K-S) law, we find that the star formation rates (SFRs) in the CNRs of most Seyfert galaxies are suppressed in this sample. Feedback is suggested to explain the suppressed SFRs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/310/210
- Title:
- Stellar composition of CMa R1
- Short Name:
- J/MNRAS/310/210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This directory contains movies in mpeg format which show models for the time evolution of the Hertzsprung-Russell diagram of a very young open cluster between 0 and 30Myr. Four different star formation scenario's are considered, (a) instantaneous star formation, (b) constant rate of star formation with time, (c) increasing rate of star formation, and (d) decreasing rate of star formation. For the latter three scenario's, models for a duration of the star formation episode {delta}t of 0.1, 1.0 and 10Myr are computed.
- ID:
- ivo://CDS.VizieR/J/A+A/471/795
- Title:
- Stellar population ages and metallicities from colors
- Short Name:
- J/A+A/471/795
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two important stellar-population parameters (age and metallicity) of the dominant stellar populations (DSPs) of galaxies are usually estimated by comparing the observed absorption line indices or colors to predictions of some simple stellar population models. However, some studies show that there is actually recent star formation in galaxies, including early type ones. This suggests that we may not be obtaining accurate the two stellar-population parameters for the DSPs of galaxies. This is obvious when we estimate the two parameters by colors, because the youngest populations dominate the light and make the fitted stellar populations younger and richer in metal. We study how young populations (YSPs) in composite stellar populations (CSPs) affect the colors of star systems and to analyze how the stellar ages and metallicities derived from colors possibly deviate from those of the DSPs. It is found that the age and mass fraction of a YSP affect colors of a mixed star system significantly, but the former is stronger. In addition, our results show that the stellar ages and metallicities derived directly from a pair of colors are about 2.14Gyr younger, while 0.0027 more metal rich on average than those of the DSPs of composite stellar systems. Some possible distributions of the differences between stellar-population parameters determined by colors and those of DSPs of CSPs are presented. The possible distributions of the differences between colors of CSPs and those of their DSPs are also shown. Stellar ages and metallicities measured by colors and line-strength indices are compared in the work, with a sample of 18 galaxies. Furthermore, the YSPs may affect the fundamental plane and Kormendy relation of early type galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/111
- Title:
- Stellar yields of rotating first stars. II.
- Short Name:
- J/ApJ/857/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent theory predicts that first stars are born with a massive initial mass of >~100M_{sun}_. Pair-instability supernova (PISN) is a common fate for such massive stars. Our final goal is to prove the existence of PISNe and thus the high-mass nature of the initial mass function in the early universe by conducting abundance profiling, in which properties of a hypothetical first star is constrained by metal-poor star abundances. In order to determine reliable and useful abundances, we investigate the PISN nucleosynthesis taking both rotating and nonrotating progenitors for the first time. We show that the initial and CO core mass ranges for PISNe depend on the envelope structures: nonmagnetic rotating models developing inflated envelopes have a lower shifted CO mass range of ~70-125_M{sun}_, while nonrotating and magnetic rotating models with deflated envelopes have a range of ~80-135_M{sun}_. However, we find no significant difference in explosive yields from rotating and nonrotating progenitors, except for large nitrogen production in nonmagnetic rotating models. Furthermore, we conduct the first systematic comparison between theoretical yields and a large sample of metal-poor star abundances. We find that the predicted low [Na/Mg]~-1.5 and high [Ca/Mg]~0.5-1.3 abundance ratios are the most important to discriminate PISN signatures from normal metal-poor star abundances, and confirm that no currently observed metal-poor star matches with the PISN abundance. An extensive discussion on the nondetection is presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/692/L9
- Title:
- Tidal evolution of transiting extrasolar planets
- Short Name:
- J/ApJ/692/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the tidal stability of extrasolar systems harboring a transiting planet and demonstrate that, independently of any tidal model, none, but one (HAT-P-2b) of these planets has a tidal equilibrium state, which implies ultimately a collision of these objects with their host star. Consequently, conventional circularization and synchronization timescales cannot be defined because the corresponding states do not represent the endpoint of the tidal evolution. Using numerical simulations of the coupled tidal equations for the spin and orbital parameters of each transiting planetary system, we confirm these predictions and show that the orbital eccentricity and the stellar obliquity do not follow the usually assumed exponential relaxation but instead decrease significantly, eventually reaching a zero value only during the final runaway merging of the planet with the star. The only characteristic evolution timescale of all rotational and orbital parameters is the lifetime of the system, which crucially depends on the magnitude of tidal dissipation within the star. These results imply that the nearly circular orbits of transiting planets and the alignment between the stellar spin axis and the planetary orbit are unlikely to be due to tidal dissipation. Other dissipative mechanisms, for instance interactions with the protoplanetary disk, must be invoked to explain these properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/170
- Title:
- Tracers of stellar mass-loss. II.
- Short Name:
- J/ApJ/856/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present integrated colors and surface brightness fluctuation magnitudes in the mid-infrared (IR), derived from stellar population synthesis models that include the effects of the dusty envelopes around thermally pulsing asymptotic giant branch (TP-AGB) stars. The models are based on the Bruzual & Charlot CB* isochrones; they are single-burst, range in age from a few Myr to 14Gyr, and comprise metallicities between Z=0.0001 and Z=0.04. I compare these models to mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. I find that models with a higher than fiducial mass-loss rate are needed to fit the mid-IR colors of "extreme" single AGB stars in the Large Magellanic Cloud. Surface brightness fluctuation magnitudes are quite sensitive to metallicity for 4.5{mu}m and longer wavelengths at all stellar population ages, and powerful diagnostics of mass-loss rate in the TP-AGB for intermediate-age populations, between 100Myr and 2-3Gyr.
