Pegasus W: An Ultrafaint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization

McQuinn, Kristen B. W.; Mao, Yao-Yuan; Buckley, Matthew R.; Shih, David; Cohen, Roger E.; Dolphin, Andrew E.

doi:10.3847/1538-4357/acaec9

Cited by 17 publications

(13 citation statements)

References 80 publications

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“…Generally extended SFHs, in excess of what is observed around the MW, have previously been obtained for other, more luminous M31 satellites from deep HST imaging (Weisz et al 2014c;Monelli et al 2016;Skillman et al 2017). Similar tentative conclusions were previously reached for a larger M31 satellite sample (including some of the UFDs) based on SFHs from much shallower photometry (Weisz et al 2014a(Weisz et al , 2019McQuinn et al 2023). These SFHs necessarily have larger uncertainties in their SFHs, prohibiting the type of concrete conclusions we are able to draw in this paper.…”

Section: Do M31's Ufd Satellites Have Extended Sfhs?supporting

confidence: 84%

“…However, the first isolated UFD was discovered serendipitously and only within the past year (Sand et al 2022). Instead, the only known UFDs that reside outside the MW halo, and that we can image down to the oMSTO, are satellites of M31 (e.g., Martin et al 2016;Collins et al 2022a;Martínez-Delgado et al 2022;McQuinn et al 2023). Measuring precise SFHs of these faint, distant systems (D ∼ 750 kpc) requires the excellent angular resolution and sensitivity of the Hubble Space Telescope (HST) and was a main science driver behind the 244 orbit HST Survey of M31 Satellites program awarded in Cycle 27 (HST- GO-15902, PI: Weisz).…”

Section: Introductionmentioning

confidence: 99%

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The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

Savino,

Weisz,

Skillman

et al. 2023

ApJ

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We present the lifetime star formation histories (SFHs) for six ultrafaint dwarf (UFD; M V > − 7.0, 4.9 < log 10 ( M * ( z = 0 ) / M ⊙ ) < 5.5 ) satellite galaxies of M31 based on deep color–magnitude diagrams constructed from Hubble Space Telescope imaging. These are the first SFHs obtained from the oldest main-sequence turnoff of UFDs outside the halo of the Milky Way (MW). We find that five UFDs formed at least 50% of their stellar mass by z = 5 (12.6 Gyr ago), similar to known UFDs around the MW, but that 10%–40% of their stellar mass formed at later times. We uncover one remarkable UFD, And xiii, which formed only 10% of its stellar mass by z = 5, and 75% in a rapid burst at z ∼ 2–3, a result that is robust to choices of underlying stellar model and is consistent with its predominantly red horizontal branch. This “young” UFD is the first of its kind and indicates that not all UFDs are necessarily quenched by reionization, which is consistent with predictions from several cosmological simulations of faint dwarf galaxies. SFHs of the combined MW and M31 samples suggest reionization did not homogeneously quench UFDs. We find that the least-massive MW UFDs (M *(z = 5) ≲ 5 × 104 M ⊙) are likely quenched by reionization, whereas more-massive M31 UFDs (M *(z = 5) ≳ 105 M ⊙) may only have their star formation suppressed by reionization and quench at a later time. We discuss these findings in the context of the evolution and quenching of UFDs.

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Section: Do M31's Ufd Satellites Have Extended Sfhs?supporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

Savino,

Weisz,

Skillman

et al. 2023

ApJ

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“…The oMSTO feature helps to break the age-metallicity degeneracy for older-age stars in a CMD, thereby facilitating robust SFH recovery with temporal resolution as fine as log(δt) = 0.05 at the oldest lookback times. These SFHs characterize the properties of satellite galaxies around the Milky Way and M31, including investigating quenching timescales and possible host-galaxy dependencies (e.g., Monelli et al 2010;Weisz et al 2014;Skillman et al 2017;Weisz et al 2019;Sacchi et al 2021;McQuinn et al 2023aMcQuinn et al , 2023bSavino et al 2023). SFHs of the Large and Small Magellanic Clouds from similarly deep HST data and ground-based data have revealed synchronized bursts of star formation that are likely interaction-driven (Harris & Zaritsky 2009;Weisz et al 2013;Massana et al 2022).…”

Section: Hst's Sfh Legacymentioning

confidence: 99%

The JWST Resolved Stellar Populations Early Release Science Program. IV. The Star Formation History of the Local Group Galaxy WLM

McQuinn,

B. Newman,

Savino

et al. 2024

ApJ

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We present the first star formation history (SFH) and age–metallicity relation (AMR) derived from resolved stellar populations imaged with the JWST NIRCam instrument. The target is the Local Group star-forming galaxy WLM at 970 kpc. The depth of the color–magnitude diagram (CMD) reaches below the oldest main sequence turnoff with a signal-to-noise ratio = 10 at M F090W = + 4.6 mag. This is the deepest CMD for any galaxy that is not a satellite of the Milky Way. We use Hubble Space Telescope (HST) optical imaging that overlaps with the NIRCam observations to directly evaluate the SFHs derived based on data from the two great observatories. The JWST and HST-based SFHs are in excellent agreement. We use the metallicity distribution function measured from stellar spectra to confirm the trends in the AMRs based on the JWST data. Together, these results confirm the efficacy of recovering an SFH and AMR with the NIRCam F090W−F150W filter combination, and validate the sensitivity and accuracy of stellar evolution libraries in the near-infrared relative to the optical for SFH recovery work. From the JWST data, WLM shows an early onset to star formation, followed by an extended pause post-reionization before star formation reignites, which is qualitatively similar to what has been observed in the isolated galaxies Leo A and Aquarius. Quantitatively, 15% of the stellar mass formed in the first Gyr, while only 10% formed over the next ∼5 Gyr. The stellar mass then rapidly doubled in ∼2.5 Gyr, followed by constant star formation over the last ∼5 Gyr.

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“…We note that a common approach to calculating absolute magnitude is to add up the luminosity contribution of every star and obtain an absolute magnitude for each individual mock stellar population (e.g., Martin et al 2016a;Collins et al 2022Collins et al , 2023Martínez-Delgado et al 2022;McQuinn et al 2023aMcQuinn et al , 2023b. This is in contrast to simply counting up the luminosity contribution of each individually observed star on the CMD, which gives the present-day luminosity of the system.…”

Section: Stellar Mass and Luminositymentioning

confidence: 99%

The Discovery of the Faintest Known Milky Way Satellite Using UNIONS

Smith,

Cerny,

Hayes

et al. 2024

ApJ

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We present the discovery of Ursa Major III/UNIONS 1, the least luminous known satellite of the Milky Way, which is estimated to have an absolute V-band magnitude of + 2.2 − 0.3 + 0.4 mag, equivalent to a total stellar mass of 16 − 5 + 6 M ⊙. Ursa Major III/UNIONS 1 was uncovered in the deep, wide-field Ultraviolet Near Infrared Optical Northern Survey (UNIONS) and is consistent with an old (τ > 11 Gyr), metal-poor ([Fe/H] ∼ −2.2) stellar population at a heliocentric distance of ∼10 kpc. Despite its being compact (r h = 3 ± 1 pc) and composed of few stars, we confirm the reality of Ursa Major III/UNIONS 1 with Keck II/DEIMOS follow-up spectroscopy and identify 11 radial velocity members, eight of which have full astrometric data from Gaia and are co-moving based on their proper motions. Based on these 11 radial velocity members, we derive an intrinsic velocity dispersion of 3.7 − 1.0 + 1.4 km s−1 but some caveats preclude this value from being interpreted as a direct indicator of the underlying gravitational potential at this time. Primarily, the exclusion of the largest velocity outlier from the member list drops the velocity dispersion to 1.9 − 1.1 + 1.4 km s−1, and the subsequent removal of an additional outlier star produces an unresolved velocity dispersion. While the presence of binary stars may be inflating the measurement, the possibility of a significant velocity dispersion makes Ursa Major III/UNIONS 1 a high-priority candidate for multi-epoch spectroscopic follow-ups to deduce the true nature of this incredibly faint satellite.

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Pegasus W: An Ultrafaint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization

Abstract: We report the discovery of an ultrafaint dwarf (UFD) galaxy, Pegasus W, located on the far side of the Milky Way–M31 system and outside the virial radius of M31. The distance to the galaxy is 915 − 91 … Show more

Cited by 17 publications

References 80 publications

The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

The JWST Resolved Stellar Populations Early Release Science Program. IV. The Star Formation History of the Local Group Galaxy WLM

The Discovery of the Faintest Known Milky Way Satellite Using UNIONS

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