PHAT. XIX. The Ancient Star Formation History of the M31 Disk

Williams, Benjamin F.; Dolphin, Andrew E.; Dalcanton, Julianne J.; Weisz, Daniel R.; Bell, Eric F.; Lewis, Alexia R.; Rosenfield, Philip; Choi, Yumi; Skillman, Evan D.; Monachesi, Antonela

doi:10.3847/1538-4357/aa862a

Cited by 102 publications

(162 citation statements)

References 57 publications

(104 reference statements)

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“…Several models have posited a major merger between M31 and (what would have been) the third largest member of the LG ∼2-4 Gyr ago (e.g., Hammer et al 2018;D'Souza & Bell 2018). These models can qualitatively explain some observed features of M31, such as a global burst of star formation 2-4 Gyr ago (e.g., Bernard et al 2015;Williams et al 2017) and the metal-rich inner halo. For example, D' Souza & Bell (2018) hypothesize such an interaction between M31 and M32p (the putative progenitor of M32) could explain the metal-rich component of M31's halo and the unusually compact nature of M32.…”

Section: Resultsmentioning

confidence: 99%

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Weisz

Martín

Dolphin

et al. 2019

ApJL

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We present the star formation histories (SFHs) of 20 faint M31 satellites (−12 M V −6) that were measured by modeling sub-horizontal branch (HB) depth color-magnitude diagrams constructed from Hubble Space Telescope (HST) imaging. Reinforcing previous results, we find that virtually all galaxies quenched between 3 and 9 Gyr ago, independent of luminosity, with a notable concentration 3 − 6 Gyr ago. This is in contrast to the Milky Way (MW) satellites, which are generally either faint with ancient quenching times or luminous with recent (<3 Gyr) quenching times. We suggest that systematic differences in the quenching times of M31 and MW satellites may be a reflection of the varying accretion histories of M31 and the MW. This result implies that the formation histories of low-mass satellites may not be broadly representative of low-mass galaxies in general. Among the M31 satellite population we identify two distinct groups based on their SFHs: one with exponentially declining SFHs (τ ∼ 2 Gyr) and one with rising SFHs with abrupt quenching. We speculate how these two groups could be related to scenarios for a recent major merger involving M31. The Cycle 27 HST Treasury survey of M31 satellites will provide well-constrained ancient SFHs to go along with the quenching times we measure here. The discovery and characterization of M31 satellites with M V −6 would help quantify the relative contributions of reionization and environment to quenching of the lowest-mass satellites.

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Section: Resultsmentioning

confidence: 99%

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Weisz

Martín

Dolphin

et al. 2019

ApJL

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“…Finally, Pezzulli et al (2015) measured the instantaneous mass and radial growth of the stellar disks of a sample of 35 nearby spiral galaxies that includes NGC 7793, finding clear signatures of its inside-out growth. Within the Local Group, the spatially resolved star formation history analyses of M31 from the PHAT survey (e.g., Williams et al 2017) and M33 (Barker et al 2007(Barker et al , 2011 have shown similar behaviors.…”

Section: Tablementioning

confidence: 97%

Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793^∗

Sacchi

Cignoni

Aloisi

et al. 2019

ApJ

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We present a detailed study of the flocculent spiral galaxy NGC 7793, part of the Sculptor group. By analyzing the resolved stellar populations of the galaxy, located at a distance of ∼ 3.7 Mpc, we infer for the first time its radial star formation history (SFH) from Hubble Space Telescope photometry, thanks to both archival and new data from the Legacy ExtraGalactic UV Survey. We determine an average star formation rate (SFR) for the galaxy portion covered by our F555W and F814W data of 0.23 ± 0.02 M /yr over the whole Hubble time, corresponding to a total stellar mass of (3.09 ± 0.33) × 10 9 M in agreement with previous determinations. Thanks to the new data extending to the F336W band, we are able to analyze the youngest stellar populations with a higher time resolution. Most importantly, we recover the resolved SFH in different radial regions of the galaxy; this shows an indication of a growing trend of the present-to-past SFR ratio, increasing from internal to more external regions, supporting previous findings of the inside-out growth of the galaxy.

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“…Therefore, we can only expect the C/M ratio to be a useful diagnostic if the stellar population spans the appropriate age range. Lewis et al (2015) and Williams et al (2017) estimated the spatially-resolved star-formation history (SFH) across the disk by fitting stellar evolution models to PHAT color-magnitude diagrams (CMDs). They find that there are global star formation events from ≈1.5-4 Gyr and at ages 8 Gyr.…”

Section: Agementioning

confidence: 99%

A Dramatic Decrease in Carbon Star Formation in M31

Boyer¹,

Williams

Aringer

et al. 2019

ApJ

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We analyze resolved stellar near-infrared photometry of 21 HST fields in M31 to constrain the impact of metallicity on the formation of carbon stars. Observations of nearby galaxies show that the carbon stars are increasingly rare at higher metallicity. Models indicate that carbon star formation efficiency drops due to the decrease in dredge-up efficiency in metal-rich thermally-pulsing Asymptotic Giant Branch (TP-AGB) stars, coupled to a higher initial abundance of oxygen. However, while models predict a metallicity ceiling above which carbon stars cannot form, previous observations have not yet pinpointed this limit. Our new observations reliably separate carbon stars from M-type TP-AGB stars across 2.6-13.7 kpc of M31's metal-rich disk using HST WFC3/IR medium-band filters. We find that the ratio of C to M stars (C/M) decreases more rapidly than extrapolations of observations in more metal-poor galaxies, resulting in a C/M that is too low by more than a factor of 10 in the innermost fields and indicating a dramatic decline in C star formation efficiency at metallicities higher than [M/H] ≈ −0.1 dex. The metallicity ceiling remains undetected, but must occur at metallicities higher than what is measured in M31's inner disk ([M/H] +0.06 dex).

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PHAT. XIX. The Ancient Star Formation History of the M31 Disk

Cited by 102 publications

References 57 publications

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793^∗

A Dramatic Decrease in Carbon Star Formation in M31

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PHAT. XIX. The Ancient Star Formation History of the M31 Disk

Cited by 102 publications

References 57 publications

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies

Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793∗

A Dramatic Decrease in Carbon Star Formation in M31

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Product

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Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793^∗