Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Sand, David J.; Mutlu-Pakdil, Burçin; Jones, M. G. K.; Karunakaran, Ananthan; Wang, Feige; Yang, Jinyi; Chiti, Anirudh; Bennet, Paul; Crnojević, Denija; Spekkens, Kristine

doi:10.3847/2041-8213/ac85ee

“…The majority of the galaxies discovered lie in close proximity to the Milky Way (MW) and the Large Magellanic Cloud, as intrinsically faint systems are more readily detected at closer distances. A smaller number have been identified as part of the M31 satellite system, found via the targeted PAndAS observations (McConnachie et al 2009) or from DESI data (Collins et al 2022) and, more recently, a galaxy was found outside the Local Group (Sand et al 2022).…”

Section: Introductionmentioning

confidence: 99%

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

McQuinn¹,

Mao²,

Buckley³

et al. 2023

ApJ

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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 + 60 kpc, measured using the luminosity of horizontal branch stars identified in Hubble Space Telescope optical imaging. The galaxy has a half-light radius (r h ) 100 − 13 + 11 pc, M V = − 7.20 − 0.16 + 0.17 mag, and a present-day stellar mass 6.5 − 1.4 + 1.1 × 10 4 M ⊙. We identify sources in the color–magnitude diagram (CMD) that may be younger than ∼500 Myr, suggesting late-time star formation in the UFD galaxy, although further study is needed to confirm these are bona fide young stars in the galaxy. Based on fitting the CMD with stellar evolution libraries, Pegasus W shows an extended star formation history. Using the τ 90 metric (defined as the timescale by which the galaxy formed 90% of its stellar mass), the galaxy was quenched only 7.4 − 2.6 + 2.2 Gyr ago, which is similar to the quenching timescale of a number of UFD satellites of M31 but significantly more recent than the UFD satellites of the Milky Way. Such late-time quenching is inconsistent with the more rapid timescale expected by reionization and suggests that, while not currently a satellite of M31, Pegasus W was nonetheless slowly quenched by environmental processes.

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“…Two overlap with the deep coverage with more stringent star-galaxy separation and are vetoed by that deeper data set. One candidate-M81-dw J0954+6821-is compact enough to show diffuse surface brightness; furthermore, the diffuse brightness is bluer in color than the resolved RGB stars, as is expected for a partially resolved dwarf galaxy (as the diffuse light is dominated by bluer subgiants and main-sequence turnoff stars; see, e.g., Figure 1 of Sand et al 2022). On this basis, we argue that it is a clear dwarf galaxy (brick red circle in Figure 2; Table 1).…”

Section: Ufd Candidate Identificationmentioning

confidence: 77%

“…Within or near the Local Group, there are two analogs to the relatively compact galaxy M81-dw J0954+6821: Pegasus V/ Andromeda XXXIV (D = 690 kpc; Collins et al 2022) and Tucana B (D = 1.4 Mpc; Sand et al 2022). In their relatively high luminosities and large sizes, M81-dw J1004+6835 and M81-dw J1000+6841 are most similar to Canes Venatici I/ Andromeda IX and Hercules/Andromeda XXIV, respectively.…”

Section: Candidate Propertiesmentioning

confidence: 98%

“…While the survey power of the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope will spur rapid progress in this field, current facilities (e.g., Magellan's Megacam or Subaru's Hyper Suprime-Cam (HSC)) already allow the discovery of faint (e.g., Smercina et al 2017;Okamoto et al 2019, in the M81 group) and ultrafaint (e.g., Mutlu-Pakdil et al 2022;Sand et al 2022) galaxies in the Local Volume (D < 5 Mpc). The M81 group (D = 3.6 Mpc; Radburn-Smith et al 2011) is particularly interesting to study.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion

Bell

¹

,

Smercina

²

,

Price

³

et al. 2022

ApJL

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The faint and ultrafaint dwarf galaxies in the Local Group form the observational bedrock upon which our understanding of small-scale cosmology rests. In order to understand whether this insight generalizes, it is imperative to use resolved-star techniques to discover similarly faint satellites in nearby galaxy groups. We describe our search for ultrafaint galaxies in the M81 group using deep ground-based resolved-star data sets from Subaru’s Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the M81 group and identify five additional extremely low surface brightness candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to M V ∼ − 6 (similar to current limits for Andromeda satellites). These candidates’ luminosities and sizes are similar to known Local Group dwarf galaxies Tucana B, Canes Venatici I, Hercules, and Boötes I. Most of these candidates are likely to be real, based on tests of our techniques on blank fields. Intriguingly, all of these candidates are spatially clustered around NGC 3077, which is itself an M81 group satellite in an advanced state of tidal disruption. This is somewhat surprising, as M81 itself and its largest satellite M82 are both substantially more massive than NGC 3077 and, by virtue of their greater masses, would have been expected to host as many or more ultrafaint candidates. These results lend considerable support to the idea that satellites of satellites are an important contribution to the growth of satellite populations around Milky Way–mass galaxies.

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“…The majority of the galaxies discovered lie in close proximity to the Milky Way (MW) and the Large Magellanic Cloud (LMC), as intrinsically faint systems are more readily detected at closer distances. A smaller number have been identified as part of the M31 satellite system, found via the targeted PAn-dAS observations (McConnachie et al 2009) or from DESI data (Collins et al 2022), and, more recently, a galaxy was found outside the Local Group (Sand et al 2022).…”

Section: Introductionmentioning

confidence: 99%

Pegasus W: An Ultra-Faint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization

McQuinn¹,

Mao²,

Buckley³

et al. 2023

Preprint

0

View full text Add to dashboard Cite

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 +60−91 kpc, measured using the luminosity of horizontal branch (HB) stars identified in Hubble Space Telescope optical imaging. The galaxy has a half-light radius (r h ) of 100 +11 −13 pc, M V = −7.20 +0.17 −0.16 mag, and a present-day stellar mass of 6.5 +1.1 −1.4 ×10 4 M . We identify sources in the color-magnitude diagram (CMD) that may be younger than ∼ 500 Myr suggesting late-time star formation in the UFD galaxy, although further study is needed to confirm these are bona fide young stars in the galaxy. Based on fitting the CMD with stellar evolution libraries, Pegasus W shows an extended star formation history (SFH). Using the τ 90 metric (defined as the timescale by which the galaxy formed 90% of its stellar mass), the galaxy was quenched only 7.4 +2.2 −2.6 Gyr ago, which is similar to the quenching timescale of a number of UFD satellites of M31 but significantly more recent than the UFD satellites of the Milky Way. Such late-time quenching is inconsistent with the more rapid timescale expected by reionization and suggests that, while not currently a satellite of M31, Pegasus W was nonetheless slowly quenched by environmental processes.

show abstract

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Cited by 30 publications

References 111 publications

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

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

Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion

Pegasus W: An Ultra-Faint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization

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