A New Milky Way Satellite Discovered in the Subaru/Hyper Suprime-Cam Survey

Homma, Daisuke; Chiba, Masashi; Okamoto, Sakurako; Komiyama, Yutaka; Tanaka, Masayuki; Tanaka, Mikito; Ishigaki, Miho N.; Akiyama, Masayuki; Arimoto, N.; Garmilla, José A.; Lupton, Robert H.; Strauss, Michael A.; Furusawa, Hisanori; Miyazaki, Satoshi; Murayama, Hitoshi; Nishizawa, Atsushi J.; Takada, Masahiro; Usuda, Tomonori; Wang, Shiang‐Yu

doi:10.3847/0004-637x/832/1/21

Cited by 98 publications

(85 citation statements)

References 43 publications

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“…The combination of the superb image quality (∼ 0 ′′ .6) and depth (i ∼ 26) and the fact that it is a multi-band survey allows us to identify UFDs at large distances, filling in the parameter space unexplored by previous surveys. We have discovered two UFDs thus far, Virgo I and Cetus III, as reported in Homma et al (2016) and Homma et al (2018). The current paper presents the discovery of another UFD and a likely globular cluster from our continuing search.…”

Section: Introductionsupporting

confidence: 78%

Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem

Homma

Chiba

Komiyama

et al. 2019

Publications of the Astronomical Society of Japan

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We report on the discovery of a new Milky Way (MW) satellite in Boötes based on data from the on-going Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). This satellite, named Boötes IV, is the third ultra-faint dwarf that we have discovered in the HSC-SSP. We have identified a statistically significant (32.3σ) overdensity of stars having characteristics of a metalpoor, old stellar population. The distance to this stellar system is D ⊙ = 209 +20 −18 kpc with a V -band absolute magnitude of M V = −4.53 +0.23 −0.21 mag. Boötes IV has a half-light radius of r h = 462 +98 −84 pc and an ellipticity of 0.64 +0.05 −0.05 , which clearly suggests that this is a dwarf satellite galaxy. We also found another overdensity that appears to be a faint globular cluster with M V = −0.20 +0.59 −0.83 mag and r h = 5.9 +1.5 −1.3 pc located at D ⊙ = 46 +4 −4 kpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (2018), which combined the characteristics of the observed satellites by the Sloan Digital Sky Survey and the Dark Energy Survey with the subhalos obtained in ΛCDM models, we estimate that there should be about two MW satellites at M V ≤ 0 in the ∼ 676 deg 2 covered by HSC-SSP, whereas that area includes six satellites (Sextans, Leo IV, Pegasus III, Cetus III, Virgo I and Boötes IV).Thus, the observed number of satellites is larger than the theoretical prediction. On the face of it, we have a problem of too many satellites, instead of the well-known missing satellites problem whereby the ΛCDM theory overpredicts the number of satellites in a MW-sized halo. This may imply that the models need more refinements for the assignment of subhalos to satellites such as considering those found by the current deeper survey. Statistically more robust constraints on this issue will be brought by further surveys of HSC-SSP over the planned ∼ 1, 400 deg 2 area.

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Section: Introductionsupporting

confidence: 78%

Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem

Homma

Chiba

Komiyama

et al. 2019

Publications of the Astronomical Society of Japan

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“…Surveys like SDSS, DES, Pan-STARRS, and HSC-SSP have revealed ∼50 satellite companions around the Milky Way (MW) (e.g. Belokurov et al 2008Belokurov et al , 2010Laevens et al 2015;Drlica-Wagner et al 2015;Bechtol et al 2015;Homma et al 2016Homma et al , 2018Homma et al , 2019Koposov et al 2018;Kim & Jerjen 2015). In these cases, dwarfs are found as overdensities in star counts.…”

Section: Introductionmentioning

confidence: 99%

Wide-field Survey of Dwarf Satellite Systems around 10 Hosts in the Local Volume

Carlsten

Greco

Beaton

et al. 2020

ApJ

105

154

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We present the results of an extensive search for dwarf satellite galaxies around 10 primary host galaxies in the Local Volume (D<12 Mpc) using archival CFHT/MegaCam imaging data. The hosts span a wide range in properties, with stellar masses ranging from that of the LMC to ∼3 times that of the Milky Way (MW). The surveyed hosts are: NGC 1023, NGC 1156, NGC 2903, NGC 4258, NGC 4565, NGC 4631, NGC 5023, M51, M64, and M104. We detect satellite candidates using a consistent semi-automated detection algorithm that is optimized for the detection of low surface brightness objects. Depending on the host, our completeness limit is M g ∼ − 8 to −10 (assuming the distance of the host). We detect objects with surface brightness down to µ 0,g ∼26 mag arcsec −2 at 90% completeness. The survey areas of the six best-surveyed hosts cover most of the inner projected R < 150 kpc area, which roughly doubles the number of MW-mass hosts surveyed at this level of area and luminosity completeness. The number of detected candidates range from 1 around M64 to 33 around NGC 4258. In total, 153 candidates are found, of which 93 are new. While we defer an analysis of the satellite luminosity functions of the hosts until distance information is available for the candidates, we do show that the candidates are primarily red, spheroid systems with properties roughly consistent with known satellites in the Local Group.

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“…What then, of the one galaxy already discovered in the first 100 deg 2 of HSC data, the MV = −0.8 ± 0.9 Virgo I galaxy (Homma et al 2016)? Taking its central MV value as gospel, Figure 9 would suggest that discovery this already rules out the restricted halo occupancy model (blue lines, top central panel).…”

Section: Predicted Number Detectable In Future Surveysmentioning

confidence: 99%

“…To do this, we assume that the one galaxy already discovered in the first 100 deg 2 of data collected by the HSC lies at the detection threshold for that survey. This galaxy, Virgo I (Homma et al 2016) has an estimated distance of ∼ 87 kpc, and is one of the faintest known with an absolute magnitude MV = −0.8 ± 0.9. Using the same process described above, we add a further data point to the bottom right panel of Figure 9, and use a linear least-squares regression line fit to all three data points to give our conservative forcast on future survey performance (solid line).…”

Section: Predicted Number Detectable In Future Surveysmentioning

confidence: 99%

The upper bound on the lowest mass halo

Jethwa¹,

Erkal²,

Belokurov³

2017

Monthly Notices of the Royal Astronomical Society

181

207

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We explore the connection between galaxies and dark matter halos in the Milky Way (MW) and quantify the implications on properties of the dark matter particle and the phenomenology of low-mass galaxy formation. This is done through a probabilistic comparison of the luminosity function of MW dwarf satellite galaxies to models based on two suites of zoom-in simulations. One suite is dark-matter-only while the other includes a disk component, therefore we can quantify the effect of the MW's baryonic disk on our results. We apply numerous Stellar-Mass-Halo-Mass (SMHM) relations allowing for multiple complexities: scatter, a characteristic break scale, and subhalos which host no galaxy. In contrast to previous works we push the model/data comparison to the faintest dwarfs by modeling observational incompleteness, allowing us to draw three new conclusions. Firstly, we constrain the SMHM relation for 10 2 < M * /M < 10 8 galaxies, allowing us to bound the peak halo mass of the faintest MW satellite to M vir > 2.4 × 10 8 M (1σ). Secondly, by translating to a Warm Dark Matter (WDM) cosmology, we bound the thermal relic mass m WDM > 2.9 keV at 95% confidence, on a par with recent constraints from the Lyman-α forest. Lastly, we find that the observed number of ultra-faint MW dwarfs is in tension with the theoretical prediction that reionisation prevents galaxy formation in almost all 10 8 M halos. This can be tested with the next generation of deep imaging surveys. To this end, we predict the likely number of detectable satellite galaxies in the Subaru/HSC survey and the LSST. Confronting these predictions with future observations will be amongst our strongest tests of WDM and the effect reionisation on low-mass systems.

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A New Milky Way Satellite Discovered in the Subaru/Hyper Suprime-Cam Survey

Cited by 98 publications

References 43 publications

Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem

Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem

Wide-field Survey of Dwarf Satellite Systems around 10 Hosts in the Local Volume

The upper bound on the lowest mass halo

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