The properties of dwarf spheroidal galaxies in the Cen A group: Stellar populations, internal dynamics, and a heart-shaped Halpha ring
Oliver Müller, Katja Fahrion, Marina Rejkuba, Michael Hilker, Federico Lelli, Katharina Lutz, Marcel S. Pawlowski, Lodovico Coccato, Gagandeep S. Anand, Helmut Jerjen
备注：
16 pages, 13 figures, accepted for publication in A&A
Dwarf spheroidal galaxies (dSphs) have been extensively investigated in the Local Group, but their low luminosity and surface brightness make similar work in more distant galaxy groups challenging. Modern instrumentation unlocks the possibility of scrutinizing these faint systems in other environments, expanding the parameter space of group properties. We use MUSE spectroscopy to study the properties of 14 known or suspected dSph satellites of Cen A. Twelve targets are confirmed to be group members based on their radial velocities. Two targets are background galaxies at 50 Mpc: KK 198 is a face-on spiral galaxy, and dw1315-45 is an ultra-diffuse galaxy with an effective radius of 2300 pc. The 12 confirmed dSph members of the Cen A group have old and metal-poor stellar populations and follow the stellar metallicity-luminosity relation defined by the dwarf galaxies in the Local Group. In the three brightest dwarf galaxies (KK 197, KKs 55, and KKs 58), we identify globular clusters, as well as a planetary nebula in KK 197, although its association with this galaxy and/or the extended halo of Cen A is uncertain. Using four discrete tracers, we measure the velocity dispersion and dynamical mass of KK 197. This dSph appears dark matter dominated and lies on the radial acceleration relation of star-forming galaxies within the uncertainties. It also is consistent with predictions stemming from modified Newtonian dynamics (MOND). Surprisingly, in the dwarf KK 203 we find an extended Halpha ring. Careful examination of Hubble Space Telescope photometry reveals a very low level of star formation at ages between 30-300 Myr. The Halpha emission is most likely linked to a 40 Myr old supernova remnant, although other possibilities for its origin cannot be entirely ruled out.
The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars…
A long slit spectrum from the barred galaxy NGC 1415 has been obtained with the 2.1m Guillermo Haro telescope in Cananea, Mexico at position angle 155d (EofN) and shows the kinematics of Na I D lines (in absorption) and Halpha, 6562.8 A, [NII] 6548 A, [NII] 6584 A, [SII] 6716 A, and [SII] 6731 A lines in emission from the central regions and the disk. Our previous Halpha continuum-free imaging of the central region showed mainly two central bright Halpha knots straddling the nucleus, and Halpha emission regions along the south-east and north-west inner spiral arms. Velocities of the Na I D abs…
We select 1076 galaxies with extinction-corrected Halpha equivalent widths too large to be explained with a Kroupa (2001) IMF, and compare these with a control sample of galaxies that is matched in stellar mass, redshift and 4000 AA break strength, but with normal Halpha equivalent widths. Our goal is to study how processes such as black hole growth and energetic feedback processes from massive stars differ between galaxies with extreme central Halpha emission and galaxies with normal young central stellar populations. The stellar mass distribution of Halpha excess galaxies is peaked at 3 \tim…
Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years si…
Simulations of the clustering of cold dark matter yield dark-matter halos that have central density cusps, but observations of totally dark-matter dominated dwarf spheroidal galaxies imply that they do not have cuspy central density profiles. We use analytic calculations and numerical modelling to argue that whenever stars form, central density cusps are likely to be erased. Gas that accumulates in the potential well of an initially cuspy dark-matter halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clo…
The traditional knowledge of the mechanisms that caused the formation and evolution of early-type galaxies (ETG) in a hierarchical universe was challenged by the unexpected finding by ATLAS3D that 86% of the ETGs show signs of a fast-rotating disk. This implies a common origin of most spiral galaxies, followed by a quenching phase, while only a minority of the most massive systems are slow rotators and were likely to be the products of merger events. Our aim is to improve our knowledge on the content and distribution of ionized hydrogen and their usage to form stars in a representative sample …
For the first time we show the detailed late-stage chemical evolution history of small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high resolution (R$\sim$20000) FLAMES/GIRAFFE abundance study at ESO/VLT of 81 photometrically selected red giant branch stars in the central 25$'$ of the Fornax dwarf spheroidal galaxy. We present abundances of \alfe\ (Mg, Si, Ca and Ti), iron-peak elements (Fe, Ni and Cr) and heavy elements (Y, Ba, La, Nd and Eu). Our sample was randomly selected, and is clearly dominated by the younger and more metal rich component of Fornax wh…
Aiming at the detection of cosmological gas being accreted onto galaxies of the local Universe, we examined the Halpha emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (\musew ) with observable Halpha (redshift < 0.42). An exhaustive screening of the corresponding Halpha images led us to select 118 reliable Halpha emitting gas clouds. The signals are faint, with a surface brightness of 10**(-17.3 pm 0.3) erg/s/cm2/arcsec2. Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, te…
I consider a sample of eight pressure-supported low-surface brightness galaxies in terms of Milgrom's modified Newtonian dynamics (MOND). These objects include seven nearby dwarf spheroidal galaxies -- Sextans, Carina, Leo II, Sculptor, Draco, Leo I, Fornax, and the ultra-diffuse galaxy DF44. The objects are modelled as Milgromian isotropic isothermal spheres characterised by two parameters that are constrained by observations: the constant line-of-sight velocity dispersion and the central surface density. The velocity dispersion determines the total mass, and, with the implied mass-to-light r…
We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and previously published data. We find a steady rise in the velocity dispersion from $300^{\prime\prime}$ into the center. The integrated-light kinematics provide a velocity dispersion of $11.76\pm0.66$ km/s inside $75^{\prime\prime}$. After applying appropriate corrections to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars. Crowding corrections need to be applied when targeting individual stars in high density stel…
Large galaxies harbor massive central black holes and their feedback causes a substantial impact in their evolution. Recently, observations suggested that dwarf galaxies might host black holes in their centers, but with lower masses (intermediate-mass black holes - IMBH). The impact of such IMBHs on the evolution of the dwarf spheroidal galaxies (dSphs), however, has not been so far properly analysed. In this work, we investigate the effects of an outflow from an IMBH on the gas dynamics in dSph galaxies by means of non-cosmological, three-dimensional hydrodynamic simulations, letting the gala…
The dynamical friction timescale of massive globular clusters (GCs) in the inner regions of cuspy dark haloes in dwarf spheroidal (dSph) galaxies can be much shorter than the Hubble time. This implies that a small fraction of the GCs is expected to be caught close to the centre of these galaxies. We compare the radial distribution of GCs predicted in simple Monte Carlo models with that of a sample of $38$ spectroscopically confirmed GCs plus 17 GC candidates, associated mainly to low-luminosity dSph galaxies. If dark matter haloes follow an NFW profile, the observed number of off-center GCs at…
By means of a one-zone evolutionary model, we study the co-evolution of supermassive black holes and their host galaxies, as a function of the accretion radiative efficiency, dark matter content, and cosmological infall of gas. In particular, the radiation feedback is computed by using the self-regulated Bondi accretion. The models are characterized by strong oscillations when the galaxy is in the AGN state with a high accretion luminosity. We found that these one-zone models are able to reproduce two important phases of galaxy evolution, namely an obscured-cold phase when the bulk of star for…
One of the leading scenarios for the formation of nuclear star clusters in galaxies is related to the orbital decay of globular clusters (GCs) and their subsequent merging, though alternative theories are currently debated. The availability of high-quality data for GCs structural and orbital parameters allow to test different nuclear star cluster formation scenarios. The Fornax dwarf spheroidal (dSph) galaxy is the heaviest satellite of the Milky Way and it is the only known dwarf spheroidal hosting 5 GCs, whereas there are no clear signatures for the presence of a central massive black hole. …
We present a detailed study of the shape of the innermost part of the rotation curves of a sample of 29 nearby spiral galaxies, based on high angular and spectral resolution kinematic Halpha Fabry-Perot observations. In particular, we quantify the steepness of the rotation curve by measuring its slope dRvc(0). We explore the relationship between the inner slope and several galaxy parameters, such as stellar mass, maximum rotational velocity, central surface brightness (μ0), bar strength and bulge-to-total ratio. Even with our limited dynamical range, we find a trend for low-mass galaxies to ex…
We present wide-field $g$ and $i$ band stellar photometry of the Sextans dwarf spheroidal galaxy and its surrounding area out to four times its half-light radius ($r_h=695\,$pc), based on images obtained with the Dark Energy Camera at the 4-m Blanco telescope at CTIO. We find clear evidence of stellar substructure associated with the galaxy, extending to a distance of $82\arcmin$ (2\,kpc) from its centre. We perform a statistical analysis of the over-densities and find three distinct features, as well as an extended halo-like structure, to be significant at the $99.7\%$ confidence level or hig…
We derive average radial gradients in the dust attenuation towards HII regions in 609 galaxies at z~1.4, using measurements of the Balmer decrement out to r~3kpc. The Balmer decrements are derived from spatially resolved maps of Halpha and Hbeta emission from the 3D-HST survey. We find that with increasing stellar mass (M) both the normalization and strength of the gradient in dust attenuation increases. Galaxies with a mean mass of <log(M)> = 9.2Msun have little dust attenuation at all radii, whereas galaxies with <log(M)>= 10.2Msun have dust attenuation toward Halpha A(Halpha)~2mag in their …
We present the star formation history (SFH) of the Sculptor dwarf spheroidal galaxy based on deep g,r photometry taken with DECam at the Blanco telescope, focusing our analysis on the central region of the galaxy extended up to $\sim 3$ core radii. We have investigated how the SFH changes radially, subdividing the sampled area into four regions, and have detected a clear trend of star formation. All the SFHs show a single episode of star formation, with the innermost region presenting a longer period of star formation of $\sim 1.5$ Gyr and for the outermost region the main period of star forma…
A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal "main-sequence" star forming galaxies. Many processes have been advocated as responsible for such a trend (also known as mass quenching), e.g., feedback from active galactic nuclei (AGNs), and the formation of classical bulges. We determine a refined star formation versus stellar mass relation in the local Universe. To this aim we use the Halpha narrow-band imaging follow-up survey (Halpha3) of field galaxies selected from the HI Arecibo Legacy Fast ALFA Surve…
Dwarf spheroidal galaxies of the Local Group obey a relationship between the line-of-sight velocity dispersion and half-light radius, although there are a number of dwarfs that lie beneath this relation with suppressed velocity dispersion. The most discrepant of these (in the Milky Way) is the `feeble giant' Crater II. Using analytic arguments supported by controlled numerical simulations of tidally-stripped flattened two-component dwarf galaxies, we investigate interpretations of Crater II within standard galaxy formation theory. Heavy tidal disruption is necessary to explain the velocity-dis…
Stellar evolution models require initial isotopic abundance sets as input, but these abundances are incomplete outside the solar neighborhood, are challenging to infer from elemental observations, and are galaxy specific. Compositions different from the Milky Way (MW) have distinct chemical histories and are important to explore. We present an isotopic history model for the Sculptor dwarf spheroidal galaxy (dSph) based on astrophysical processes, using a complementary approach to GCE models, which can estimate isotopic abundances for future nucleosynthesis studies. We approximated the isotopic…
We present a study of short period, central helium-burning variable stars in the Local Group dwarf spheroidal galaxy LeoI, including 106 RR Lyrae stars and 51 Cepheids. So far, this is the largest sample of Cepheids and the largest Cepheids to RR Lyrae ratio found in such a kind of galaxy. The comparison with other Local Group dwarf spheroidals, Carina and Fornax, shows that the period distribution of RR Lyrae stars is quite similar, suggesting similar properties of the parent populations, whereas the Cepheid period distribution in LeoI peaks at longer periods (P \sim 1.26d instead of ~0.5d) a…
We report ALMA observations of $^{12}$CO(3-2) and $^{13}$CO(3-2) in the gas-poor dwarf galaxy NGC 5253. These 0.3"(5.5 pc) resolution images reveal small, dense molecular gas clouds that are located in kinematically distinct, extended filaments. Some of the filaments appear to be falling into the galaxy and may be fueling its current star formation. The most intense CO(3-2) emission comes from the central $\sim$100 pc region centered on the luminous radio-infrared HII region known as the supernebula. The CO(3-2) clumps within the starburst region are anti-correlated with H$α$ on $\sim$5 pc sca…
We study the density structures of dark matter subhalos for both cold dark matter and self-interacting dark matter models using high-resolution cosmological $N$-body simulations. We quantify subhalo's central density at 150 pc from the center of each subhalo at the classical dwarf spheroidal and ultrafaint dwarf scales found in Milky-Way sized halos. By comparing them with observations, we find that the self-interacting scattering cross-section of $σ/m<3\ \rm{cm^{2}g^{-1}}$ is favored. Due to the combination of hosts' tide and self-interactions, the central density of subhalos with small peric…
In this letter, we report the discovery of an intriguing HVS (J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age $\sim14.0$ Gyr and [Fe/H] $= -2.23$ dex) and has a total velocity of $559.01^{+135.07}_{-87.40}$ km s$^{-1}$ in the Galactic rest-frame and a heliocentric distance of $2.90^{+0.72}_{-0.48}$ kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting it a promising HVS candidate. By reconstructing its trajectory in the Galactic …
We use the fundamental-mode RR Lyr-type variable stars (RRab) from OGLE-IV survey to draw a 3D picture of the central part of the tidally disrupted Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. We estimate the line-of-sight thickness of the Sgr dSph stream to be FWHM_cen=2.42 kpc. Based on OGLE-IV observations collected in seasons 2011-2014 we conduct a comprehensive study of stellar variability in the field of the globular cluster M54 (NGC 6715) residing in the core of this dwarf galaxy. Among the total number of 268 detected variable stars we report the identification of 174 RR Lyr stars, …
We present the Star Formation History (SFH) and the age-metallicity relation (AMR) in three fields of the Fornax dwarf spheroidal galaxy. They sample a region spanning from the centre of the galaxy to beyond one core radius, which allows studying galactocentric gradients. In all the cases, we found stars as old as 12 Gyr, together with intermediate-age and young stellar populations. The last star formation events, as young as 1 Gyr old, are mainly located in the central region, which may indicate that the gas reservoir in the outer parts of the galaxy would have been exhausted earlier than in …
The center of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) hosts a nuclear star cluster, M54, which is the only galaxy nucleus that can be resolved into individual stars at optical wavelengths. It is thus a key target for understanding the formation of nuclear star clusters and their relation to globular clusters. We present a large Multi-Unit Spectroscopic Explorer (MUSE) data set that covers M54 out to $\sim$2.5 half-light radius, from which we extracted the spectra of $\sim$6600 cluster member stars. We use these data in combination with HST photometry to derive age and metallicity fo…
We present a significantly improved version of our numerical code JASMINE, that can now solve the Jeans equations for axisymmetric models of stellar systems, composed of an arbitrary number of stellar populations, a Dark Matter halo, and a central Black Hole. The stellar components can have different structural (density profile, flattening, mass, scale length), dynamical (rotational support, velocity dispersion anisotropy), and population (age, metallicity, Initial Mass Function, mass-to-light ratio) properties. These models, when combined with observations, will allow to investigate important…
Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we characterize the spatial distribution of star formation in 76 high star forming galaxies in 10 clusters at 0.3< z <0.7. All these galaxies are likely restricted to first infall. In a companion paper we contrast the properties of field and cluster galaxies, whereas here we correlate the properties of Hα emitters to a number of tracers of the cluster environment to investigate its role in driving galaxy transformations. Hα emitters are found in the clusters out to 0.5 virial radii, the maximum radius covered by GLASS. …
We use a cosmological simulation of the formation of the Local Group to explore the origin of age and metallicity gradients in dwarf spheroidal galaxies. We find that a number of simulated dwarfs form "outside-in", with an old, metal-poor population that surrounds a younger, more concentrated metal-rich component, reminiscent of dwarf spheroidals like Sculptor or Sextans. We focus on a few examples where stars form in two populations distinct in age in order to elucidate the origin of these gradients. The spatial distributions of the two components reflect their diverse origin; the old stellar…
We present medium-resolution spectra of 16 radial velocity red-giant members of the low-luminosity Bootes I dwarf spheroidal (dSph) galaxy, that have sufficient S/N for abundance determination, based on the strength of the Ca II K line. Assuming [Ca/Fe] ~ +0.3, the abundance range in the sample is Delta [Fe/H] ~ 1.7 dex, with one star having [Fe/H] = -3.4. The dispersion is sigma([Fe/H]) = 0.45 +/- 0.08 -- similar to those of the Galaxy's more luminous dSph systems and Omega Centauri. This suggests that the large mass (greater than approximately 10 million solar masses) normally assumed to fos…
A new family of self-consistent DF-based models of stellar systems is explored. The stellar component of the models is described by a distribution function (DF) depending on the action integrals, previously used to model the Fornax dwarf spheroidal galaxy (dSph). The stellar component may cohabit with either a dark halo, also described by a DF, or with a massive central black hole. In all cases we solve for the model's self-consistent potential. Focussing on spherically symmetric models, we show how the stellar observables vary with the anisotropy prescribed by the DF, with the dominance and n…
We analyze in detail the spatial distribution and kinematic properties of two different stellar populations in Andromeda II (And II) dwarf spheroidal galaxy. We obtained their detailed surface density maps, together with their radial density profiles. The two populations differ not only in age and metallicity, but also in their spatial distribution and kinematics. Old stars ($\gtrsim 11$ Gyr) follow a round distribution well fitted by truncated density profiles. These stars rotate around the projected optical major axis of the galaxy with line-of-sight velocities $v_{los}(r_h) = 16 \pm 3$ km s…
We present Iron, Magnesium, Calcium, and Titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0 arcmin ~70 pc from the center) from medium-resolution Keck/DEIMOS spectra. All the considered stars belong to the massive globular cluster M54 or to the central nucleus of the galaxy (Sgr,N). In particular we provide abundances for 109 stars with [Fe/H] > -1.0, more than doubling the available sample of spectroscopic metallicity and alpha-elements abundance estimates for Sgr dSph stars in this metallicity regime. Also, we find the first confirm…
We apply a flexible parametric model, a combination of generalized Plummer profiles, to infer the shapes of the stellar density profiles of the Milky Way's satellite dwarf spheroidal galaxies (dSphs). We apply this model to 40 dSphs using star counts from the Sloan Digital Sky Survey, PanStarrs-1 Survey, Dark Energy Survey, and Dark Energy Camera Legacy Survey. Using mock data, we examine systematic errors associated with modelling assumptions and identify conditions under which our model can identify `non-standard' stellar density profiles that have central cusps and/or steepened outer slopes…
We present a method for identifying localized secondary populations in stellar velocity data using Bayesian statistical techniques. We apply this method to the dwarf spheroidal galaxy Ursa Minor and find two secondary objects in this satellite of the Milky Way. One object is kinematically cold with a velocity dispersion of $4.25 \pm 0.75\ \kms$ and centered at $(9.1\arcmin \pm 1.5, 7.2\arcmin \pm 1.2)$ in relative RA and DEC with respect to the center of Ursa Minor. The second object has a large velocity offset of $-12.8^{+1.75}_{-1.5}\ \kms$ compared to Ursa Minor and centered at $(-14.0\arcm…
We present the spectral analysis of an 87~ks \emph{XMM-Newton} observation of Draco, a nearby dwarf spheroidal galaxy. Of the approximately 35 robust X-ray source detections, we focus our attention on the brightest of these sources, for which we report X-ray and multiwavelength parameters. While most of the sources exhibit properties consistent with AGN, few of them possess characteristics of LMXBs and CVs. Our analysis puts constraints on population of X-ray sources with $L_X>3\times10^{33}$~erg~s$^{-1}$ in Draco suggesting that there are no actively accreting BH and NS binaries. However, we …
Although still under debate, observations generally suggest that dwarf spheroidal (dSph) galaxies exhibit large constant-density cores in the centers, which can hardly be explained by dissipationless cold dark matter simulations without baryonic feedback. Wave dark matter (${ψ{\rm DM}}$), characterized by a single parameter, the dark matter particle mass $m_ψ$, predicts a central soliton core in every galaxy arising from quantum pressure against gravity. Here we apply Jeans analysis assuming a soliton core profile to the kinematic data of eight classical dSphs so as to constrain $m_ψ$, and obt…
Using deep V, B-V wide-field photometry, we have conducted a new study of stellar over-densities in the Fornax dwarf spheroidal galaxy by determining detailed Star Formation Histories from Colour-Magnitude Diagram analysis. We have concentrated on the relatively young stellar component (<4 Gyr old), and compared this to the underlying Fornax field population. We have studied in more detail the previously known inner shell-like structure and shown that it has a well-defined age-metallicity relation with a peak at ~1.5 Gyr, [Fe/H]=-0.6 dex. Comparison to the Fornax centre shows that the over-den…
We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I LRIS and Keck II DEIMOS spectrographs. Based on their g-i colors (taken with the CFHT MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the Milky Way dSph population. We a…
SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. II. Dynamics of the dust in the Mira wind and the Halpha gas in the jet
ETH Zurich, Institute for Particle Physics and Astrophysics（苏黎世联邦理工学院，粒子物理与天体物理研究所）；Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur（拉格朗日实验室，尼斯索菲亚-安蒂波利斯大学，法国国家科学研究中心，蔚蓝海岸天文台）；Université Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG）；Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille（艾克斯马赛大学，法国国家科学研究中心，LAM，马赛天体物理实验室）；LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité（LESIA，巴黎天文台，PSL研究大学，法国国家科学研究中心，索邦大学，UPMC巴黎第六大学，巴黎第七大学，索邦巴黎城）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；INAF – Osservatorio Astronomico di Padova（意大利国家天体物理研究所，帕多瓦天文台）
As is usual in dwarf spheroidal galaxies, today the Local Group galaxy Ursa Minor is depleted of its gas content. How this galaxy lost its gas is still a matter of debate. To study the history of gas loss in Ursa Minor, we conducted the first three-dimensional hydrodynamical simulations of this object, assuming that the gas loss was driven by galactic winds powered only by type II supernovae (SNe II). The initial gas setup and supernova (SN) rates used in our simulations are mainly constrained by the inferred star formation history and the observed velocity dispersion of Ursa Minor. After 3 Gy…
We present a novel strategy to uncover the Galactic population of quiescent black holes (BHs). This is based on a new concept, the photometric mass function (PMF), which opens up the possibility of an efficient identification of dynamical BHs in large fields-of-view. This exploits the width of the disc Halpha emission line, combined with orbital period information. We here show that Halpha widths can be recovered using a combination of customized Halpha filters. By setting a width cut-off at 2200 km/s we are able to cleanly remove other Galactic populations of Halpha emitters, including ~99.9%…
