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We analyzed images of every northern hemisphere Sd galaxy listed in the Third Reference Catalogue of Bright Galaxies (RC3) with a relatively face-on inclination ($\theta\leq30{\deg}$). Specifically, we measured the spiral arms' winding angle, $\phi$, in 85 galaxies. We applied a novel black hole mass planar scaling relation involving the rotational velocities (from the literature) and pitch angles of each galaxy to predict central black hole masses. This yielded 23 galaxies, each having at least a 50% chance of hosting a central intermediate-mass black hole (IMBH), $10^2$1.22% of bright galaxies ($B_{\rm T}\lesssim15.5$ mag) in the local Universe host an IMBH (i.e., the "occupation fraction"), which implies a number density $>$$4.96\times10^{-6}$ Mpc$^{-3}$ for central IMBHs. Finally, we observe that Sd galaxies exhibit an unexpected diversity of properties that resemble the general population of spiral galaxies, albeit with an enhanced signature of the eponymous prototypical traits (i.e., low masses, loosely wound spiral arms, and smaller rotational velocities)., Comment: Unedited manuscript (30 pages, 5 figures, and 1 table) accepted by The Astrophysical Journal on June 7, 2024

{We report the discovery of 20 new dwarf galaxies in the Local Volume identified as optical counterparts to the Five-hundred-meter Aperture Spherical radio Telescope (FAST) All Sky HI Survey (FASHI) sources. The galaxies have a median stellar mass of $7.8\times 10^6~M_{\odot}$ and a median HI mass of $1.0\times 10^7~M_{\odot}$. Most of them are field galaxies, while three are probable members of the M 101 and M 106 groups. We also found seven FASHI radio sources to be probable dark HI clouds in nearby groups. Together with four other known HI clouds in the local groups, their mean-square radial velocity difference of 49~km~s$^{-1}$ with respect to the host galaxies yields an average total mass of ($2.7\pm1.0)\times10^{11}~M_{\odot}$ for these groups on the projected scale of 90 kpc., Comment: 9 pages, 4 tables, 4 figures, accepted for publication in A&ALett

The interacting binary system NGC 4490/85 = Arp 269 is intermediate in mass between the Milky Way/Large Magellanic Cloud and the Large/Small Magellanic Cloud binary systems. It is a system of 14 known galaxies. We estimate the total Newtonian gravitating mass of the NGC\,4490/85 group to be M_T = (1.37 +- 0.43) times 10^{12} M_Sun using radial velocities and projected separations of its 13~candidate members. The system of dwarf satellites in the group demonstrates signs of coherent rotation in the same direction as that of the extended HI-shell surrounding the central interacting galaxy pair. The origin of this phase-space correlated population of star-forming late-type satellite galaxies raises questions in view of the planes-of-satellites observed around more massive galaxy pairs that are, however, made up of old early-type dwarf galaxies. We also report the detection of a candidate stellar Plume near the binary. This elongated structure of low surface brightness is a likely optical counterpart to the HI-tail north of NGC 4490/85, recently discovered by the FAST radio telescope., Comment: LaTeX, 7 pages, 2 figures, 2 tables, MNRAS, in press, updated for text adjustments to published version

The tip of the red giant branch (TRGB) allows for the measurement of precise and accurate distances to nearby galaxies, based on the brightest ascent of low-mass red giant branch stars before they undergo the helium flash. With the advent of JWST, there is great promise to utilize the technique to measure galaxy distances out to at least 50 Mpc, significantly further than HST's reach of 20 Mpc. However, with any standard candle, it is first necessary to provide an absolute reference. Here we use Cycle 1 data to provide an absolute calibration in the F090W filter. F090W is most similar to the F814W filter commonly used for TRGB measurements with HST, which had been adopted by the community due to minimal dependence from the underlying metallicities and ages of stars. The imaging we use was taken in the outskirts of NGC 4258, which has a direct geometrical distance measurement from the Keplerian motion of its water megamaser. Utilizing several measurement techniques, we find $M_{TRGB}^{F090W}$ = -4.362 $\pm$ 0.033 (stat) $\pm$ 0.045 (sys) mag (Vega) for the metal-poor TRGB. We also perform measurements of the TRGB in two Type Ia supernova hosts, NGC 1559, and NGC 5584. We find good agreement between our TRGB distances and previous distance determinations to these galaxies from Cepheids ($\Delta$ = 0.01 $\pm$ 0.06 mag), with these differences being too small to explain the Hubble tension ($\sim$0.17 mag). As a final bonus, we showcase the serendipitous discovery of a faint dwarf galaxy near NGC 5584., Comment: 20 pages, 12 figures, accepted to ApJ

We performed a search for faint low surface brightness dwarf galaxies around the major spiral galaxy M\,101 and in the large rectangular area within SGL = [30 -- 80]$^{\circ}$, SGB =[10 -- 37]$^{\circ}$ spanning a chain of galaxies: M\,63, M\,51, M\,101, and NGC\,6503, based on the data from DESI Legacy Imaging Surveys. Six new supposed dwarf members of the complex were discovered. We present a list of 25 prospective members of the M\,101 group and estimate the total mass and the total-mass-to-$K$-band luminosity ratio of the group as $(1.02\pm0.42)\times10^{12}~M_{\odot}$ and $(16.0\pm6.5)~M_{\odot}/L_{\odot}$, respectively. We notice that the average dark mass-to-luminosity ratio in the groups around M\,63, M\,51, and M\,101 is $(12\pm4)M_{\odot}/L_{\odot}$ that almost an order of magnitude lower than the global cosmic ratio, $(102\pm5)M_{\odot}/L_{\odot}$., Comment: 9 pages, 3 figures, 3 tables, 1 appendix. accepted to A&A

Using Hubble Space Telescope imaging of the resolved stellar population of KK~242 = NGC6503-d1 = PGC~4689184, we measure the distance to the galaxy to be $6.46\pm0.32$ Mpc and find that KK~242 is a satellite of the low-mass spiral galaxy NGC~6503 located on the edge of the Local Void. Observations with the Karl G. Jansky Very Large Array show signs of a very faint HI-signal at the position of KK~242 within a velocity range of $V_{hel} = -80\pm10$ km\,s$^{-1}$. This velocity range is severely contaminated by HI emission from the Milky Way and from NGC6503. The dwarf galaxy is classified as the transition type, dIrr/dSph, with a total HI-mass of $< 10^6 M_{\odot}$ and a star formation rate SFR(H$\alpha$) = --4.82 dex ($M{\odot}$/yr). Being at a projected separation of 31 kpc with a radial velocity difference of -- 105 km\,s$^{-1}$ relative to NGC~6503, KK~242 gives an estimate of the halo mass of the spiral galaxy to be $\log(M/M_{\odot}$) = 11.6. Besides NGC~6503, there are 8 more detached low-luminosity spiral galaxies in the Local Volume: M~33, NGC~2403, NGC~7793, NGC~1313, NGC~4236, NGC~5068, NGC~4656 and NGC~7640, from whose small satellites we have estimated the average total mass of the host galaxies and their average total mass-to-K-band-luminosity $\langle M_T/M_{\odot}\rangle = (3.46\pm0.84)\times 10^{11}$ and $(58\pm19) M_{\odot}/L_{\odot}$, respectively., Comment: Accepted for publication in the Astronomical Journal

Rapid advance has been made recently in accurate distance measurements for nearby ($D < 11$ Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way-like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass-to-$K$-band luminosity ratio is $31\pm6 M_\odot/L_\odot$ for the luminous galaxies, increasing up to $\sim200 M_\odot/L_\odot$ toward dwarfs. The bulge-dominated luminous galaxies are characterized with $\langle{}M_T/L_K\rangle = 73\pm15 M_\odot/L_\odot$, while the disc-dominated spirals have $\langle{}M_T/L_K\rangle = 17.4\pm2.8 M_\odot/L_\odot$. We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km/s and a poor dark matter halo with $\langle{}M_T/L_K\rangle = 5.5\pm1.1 M_\odot/L_\odot$. We note that a fraction of quenched (dSph, dE) companions around Milky Way-like galaxies decreases with their linear projected separation as $0.75 \exp(-R_p/350\,\mathrm{kpc})$., Comment: 20 pages, 8 figures, 7 tables. Accepted for publication in Astronomische Nachrichten

The Extragalactic Distance Database (EDD) was created as a repository for high quality, redshift-independent distances. A key component of EDD is the Color Magnitude Diagrams/Tip of the Red Giant Branch (CMDs/TRGB) catalog, which provides information on the stellar content of nearby galaxies observed with the Hubble Space Telescope (HST). Here we provide a decadal update to this catalog, which has now doubled in size to over 500 galaxies. We highlight the additions to our data reduction and analysis techniques, and provide examples of the science that has been made possible with this large data set. We find the TRGB to be a reliable measure for distance, and we aim to extend its distance coverage with HST to every galaxy within 10 Mpc. In the near-future, the combination of the James Webb Space Telescope and the Nancy Grace Roman Space Telescope will dramatically increase the number of targets within our grasp., Comment: 8 figures, 20 pages. Accepted to AJ. Materials available at edd.ifa.hawaii.edu

Two dwarf galaxies: WOC2017-07 and PGC 704814 located in the vicinity of the nearby luminous spiral galaxy NGC 253 were observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances of 3.62$\pm$0.18 Mpc and 3.66$\pm$0.18 Mpc were derived using the tip of the red giant branch method. These distances are consistent with the dwarf galaxies being members of the NGC 253 group. Based on the radial velocities and projected separations of seven assumed dwarf companions, we estimated the total mass of NGC 253 to be $(8.1\pm2.6) 10^{11} M_{\odot}$, giving a total-mass-to-$K$-luminosity ratio $M_{\rm orb}/L_K = (8.5\pm2.7) M_{\odot}/L_{\odot}$. A notable property of NGC 253 is its declined rotation curve. NGC 253 joins four other luminous spiral galaxies in the Local Volume with declined rotation curves (NGC 2683, NGC 2903, NGC 3521 and NGC 5055) that together have the low average total-mass-to-luminosity ratio, $M_{\rm orb}/L_K = (5.5\pm1.1) M_{\odot}/L_{\odot}$. This value is only $\sim$1/5 of the corresponding ratio for the Milky Way and M 31., Comment: 8 pages, 3 figures, 2 tables. Accepted to ApJ

Distances and radial velocities of galaxies in the vicinity of the luminous early-type galaxy M 104 (Sombrero) are used to derive its dark matter mass. Two dwarf galaxies: UGCA 307 and KKSG 30 situated near M 104 were observed with the Advanced Camera for Surveys on the Hubble Space Telescope. The distances $9.03^{+0.84}_{-0.51}$ Mpc (UGCA 307) and $9.72^{+0.44}_{-0.41}$ Mpc (KKSG 30) were determined using the tip of the red giant branch method. These distances are consistent with the dwarf galaxies being satellites of Sombrero. Using radial velocities and projected separations of UGCA 307, KKSG 30, and a third galaxy with an accurate distance (KKSG 29), as well as 12 other assumed companions with less accurate distances, the total mass of M 104 is estimated to be $(1.55\pm0.49) 10^{13} M_{\odot}$. At the K-band luminosity of the Sombrero galaxy of $2.4 10^{11} L_{\odot}$, its total mass-to-luminosity ratio is $M_T/L_K = (65\pm20)M_{\odot}/L_{\odot}$, which is about three times higher than that of luminous bulgeless galaxies., Comment: 6 pages, 5 figures, 3 tables, accepted to Astronomy & Astrophysics

We investigate the distribution and velocity field of galaxies situated in a band of 100 by 20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km/s. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with $M_{\rm H\,I} > M_*$ looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500-1000 km/s comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of $-$840 km/s. This cloud (or filament?) resides at a distance of 16.1 Mpc from us and approximately 5 Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km/s. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be $R_0 = (7.0\pm0.3)$ Mpc that yields the total mass of Virgo cluster to be $(7.4\pm0.9)\times 10^{14} M_{\odot}$ in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core., Comment: 19 pages, 13 figures, 4 tables. Published in Astrophysical Bulletin, Vol.73, pp.124-141 (2018)

We present observations with the Advanced Camera for Surveys on the Hubble Space Telescope of the nearby dwarf spheroidal galaxy KKH 22 = LEDA 2807114 in the vicinity of the massive spiral galaxy IC 342. We derived its distance of 3.12+-0.19 Mpc using the tip of red giant branch (TRGB) method. We also used the 6 m BTA spectroscopy to measure a heliocentric radial velocity of the globular cluster in KKH22 to be +30+-10 km/s. The dSph galaxy KKH 22 has the V-band absolute magnitude of -12.19 mag and the central surface brightness mu_v,0 = 24.1 mag/sq.arcsec. Both the velocity and the distance of KKH 22 are consistent with the dSph galaxy being gravitationally bound to IC 342. Another nearby dIr galaxy, KKH 34, with a low heliocentric velocity of +106 km/s has the TRGB distance of 7.28+-0.36 Mpc residing in the background with respect to the IC 342 group. KKH 34 has a surprisingly high negative peculiar velocity of -236+-26 km/s., Comment: 7 pages, 6 figures, accepted in A&A

Aims. This work considers the Virgo cluster of galaxies, focusing on its structure, kinematics, and morphological landscape. Our principal aim is to estimate the virial mass of the cluster. For this purpose, we present a sample of 1537 galaxies with radial velocities $V_{LG} < 2600$~km~s$^{-1}$ situated within a region of $\Delta{}SGL = 30^\circ$ and $\Delta{}SGB = 20^\circ$ around M87. About half of the galaxies have distance estimates. Methods. We selected 398 galaxies with distances in a $(17\pm5)$~Mpc range. Based on their 1D and 2D number-density profiles and their radial velocity dispersions, we made an estimate for the virial mass of the Virgo cluster. Results. We identify the infall of galaxies towards the Virgo cluster core along the Virgo Southern Extension filament. From a 1D profile of the cluster, we obtain the virial mass estimate of $(6.3\pm0.9) \times 10^{14} M_\odot, $ which is in tight agreement with its mass estimate via the external infall pattern of galaxies. Conclusions. We conclude that the Virgo cluster outskirts between the virial radius and the zero-velocity radius do not contain significant amounts of dark matter beyond the virial radius., Comment: 10 pages, 10 figures, 6 tables. Accepted for publication on Astronomy & Astrophysics

The Milky Way lies in a thin plane, the Local Sheet, a part of a wall bounding the Local Void lying toward the north supergalactic pole. Galaxies with accurate distances both above and below this supergalactic equatorial plane have systematically negative peculiar velocities. The interpretation of this situation is that the Local Void is expanding, giving members of the Local Sheet deviant velocities toward the south supergalactic pole. The few galaxies within the void are evacuating the void. Galaxies in a filament in the supergalactic south are not feeling the expansion so their apparent motion toward us is mainly a reflex of our motion. The model of the local velocity field was uncertain because the apex of our motion away from the Local Void lies in obscurity near the Galactic plane. Here, results of Hubble Space Telescope infrared observations are reported that find tip of the red giant branch distances to four obscured galaxies. All the distances are $\sim7$ Mpc, revealing that these galaxies are part of a continuous filamentary structure passing between the north and south Galactic hemispheres and sharing the same kinematic signature of peculiar velocities toward us. A fifth galaxy nearby in projection, GALFA-DW4, has an ambiguous distance. If nearby at $\sim 3$ Mpc, this galaxy has an anomalous velocity away from us of +348 km/s. Alternatively, perhaps the resolved stars are on the asymptotic giant branch and the galaxy is beyond 6 Mpc whence the observed velocity would not be unusual., Comment: 14 pages, 7 figures. Accepted for publication in ApJ

It has recently been suggested that the nearby galaxies Maffei 1 and 2 are further in distance than previously thought, such that they no longer are members of the same galaxy group as IC 342. We reanalyze near-infrared photometry from the Hubble Space Telescope, and find a distance to Maffei 2 of $5.73\pm0.40$ Mpc. With this distance, the Maffei Group lies 2.5 Mpc behind the IC 342 Group and has a peculiar velocity toward the Local Group of $-128\pm33$ km/s. The negative peculiar velocities of both of these distinct galaxy groups are likely the manifestation of void expansion from the direction of Perseus-Pisces., Comment: 6 pages, 2 figures, Accepted to ApJL (replacement adjusts/fixes luminosities in table 1)

If the extremely low surface brightness galaxy Coma P lies at $5.5\pm0.3$ Mpc as recently proposed then it would have an extraordinarily deviant peculiar velocity of $\sim900$ km $\mathrm{s^{-1}}$ at a location where differential velocities between galaxies are low. We have accessed the images from the HST archives used to derive the literature distance from the magnitude of the tip of the red giant branch. Our analysis gives the distance to be $10.9\pm1.0$ Mpc. At this location the galaxy lies within the infall region of the Virgo Cluster, such that its still considerable peculiar velocity of $\sim500$ km $\mathrm{s^{-1}}$ is consistent with an established model. Coma P has an unusually pronounced asymptotic giant branch relative to its red giant branch. The dominant stellar population is just a few Gyr old., Comment: Accepted for publication in ApJL, 7 pages, 3 figures

Tip of the red giant branch distances are acquired from Hubble Space Telescope images for 16 galaxies to the foreground of the Virgo Cluster. The new distances with 5% accuracy, combined with archival measurements, tightly constrain the near side location of the onset of infall into the Virgo Cluster to be 7.3+-0.3 Mpc from the cluster, reaching within 9 Mpc of the Milky Way. The mass within this turnaround radius about the cluster is 8.3+-0.9 x 10^{14} Msun. Color-magnitude diagrams are provided for galaxies in the study and there is brief discussion of their group affiliations., Comment: 24 pages, 5 figures, 3 tables, accepted to ApJ

Aims. We use accurate data on distances and radial velocities of galaxies around the Local Group, as well as around 14 other massive nearby groups, to estimate their radius of the zero-velocity surface, $R_0$, which separates any group against the global cosmic expansion. Methods. Our $R_0$ estimate was based on fitting the data to the velocity field expected from the spherical infall model, including effects of the cosmological constant. The reported uncertainties were derived by a Monte Carlo simulation. Results. Testing various assumptions about a location of the group barycentre, we found the optimal estimates of the radius to be $0.91\pm0.05$~Mpc for the Local Group, and $0.93\pm0.02$~Mpc for a synthetic group stacked from 14 other groups in the Local Volume. Under the standard Planck model parameters, these quantities correspond to the total mass of the group $\sim (1.6\pm0.2) 10^{12} M_{\odot}$. Thus, we are faced with the paradoxical result that the total mass estimate on the scale of $R_0 \approx (3- 4) R_{vir}$ is only $~60$% of the virial mass estimate. Anyway, we conclude that wide outskirts of the nearby groups do not contain a large amount of hidden mass outside their virial radius., Comment: 15 pages, 6 figures, 8 tables. Accepted to Astronomy & Astrophysics

We consider a sample of 412 galaxies with radial velocities $V_{\rm LG} < 2500$ km s$^{-1}$ situated in the sky region of ${\rm RA}=13^h\hspace{-0.4em}.\,0$ ... $19^h\hspace{-0.4em}.\,0$, ${\rm Dec}=+10^{\circ}$ ... $+40^{\circ}$ between the Local Void and the Supergalactic plane. One hundred and eighty-one of them have individual distance estimates. Peculiar velocities of the galaxies as a function of Supergalactic latitude SGB show signs of Virgocentric infall at $SGB < 10^{\circ}$ and motion from the Local Void at $SGB > 60^{\circ}$. A half of the Hercules-Bootes galaxies belong to 17 groups and 29 pairs, with the richest group around NGC5353. A typical group is characterized by the velocity dispersion of $67$ km s$^{-1}$, the harmonic radius of $182$ kpc, the stellar mass of $4.3 \times10^{10} M_{\odot}$ and the virial-to-stellar mass ratio of $32$. The binary galaxies have the mean radial velocity difference of $37$ km s$^{-1}$, the projected separation of $96$ kpc, the mean integral stellar mass of $2.6\times 10^9 M_{\odot}$ and the mean virial-to-stellar mass ratio of about $8$. The total dark-matter-to-stellar mass ratio in the considered sky region amounts to $37$ being almost the same as that in the Local Volume., Comment: 11 pages, 5 figures, 4 tables. Accepted to Astrophysical Bulletin

Two galaxies that lie deep within the Local Void provide a test of the expectation that voids expand. The modest (M_B~-14) HI bearing dwarf galaxies ALFAZOAJ1952+1428 and KK246 have been imaged with Hubble Space Telescope in order to study the stellar populations and determine distances from the luminosities of stars at the tip of the red giant branch. The mixed age systems have respective distances of 8.39 Mpc and 6.95 Mpc and inferred line-of-sight peculiar velocities of -114 km/s and -66 km/s toward us and away from the void center. These motions compound on the Milky Way motion of ~230 km/s away from the void. The orbits of the two galaxies are reasonably constrained by a numerical action model encompassing an extensive region that embraces the Local Void. It is unambiguously confirmed that these two void galaxies are moving away from the void center at several hundred km/s., Comment: Accepted for publication in the Astrophysical Journal

We study different incarnations of the Tully-Fisher (TF) relation for the Local Volume (LV) galaxies taken from Updated Nearby Galaxy Catalog. The UNGC sample contains 656 galaxies with $W_{50}$ HI-line-width estimates, mostly belonging to low mass dwarfs. Of them, 296 objects have distances measured with accuracy better than 10%. For the sample of 331 LV galaxies having baryonic masses $\log M_{bar} > 5.8 \log M_\odot$ we obtain a relation $\log M_{bar}= 2.49 \log W_{50} + 3.97$ with observed scatter of 0.38 dex. The largest factors affecting the scatter are observational errors in $K$-band magnitudes and $W_{50}$ line widths for the tiny dwarfs, as well as uncertainty of their inclinations. We find that accounting for the surface brightness of the LV galaxies, or their gas fraction, or specific star formation rate, or the isolation index do not reduce essentially the observed scatter on the baryonic TF-diagram. We also notice that a sample of 71 dSph satellites of the Milky Way and M31 with known stellar velocity dispersion $\sigma^*$ tends to follow nearly the same bTF relation, having slightly lower masses than that of late-type dwarfs., Comment: 36 pages, 14 figures, 5 tables. Accepted to The Astrophysical Journal

We present the observations and first results from the FIGGS2 survey. FIGGS2 is an extension of the earlier Faint Irregular Galaxies GMRT survey (FIGGS) towards faint luminosity end. The sample consists of 20 galaxies of which 15 were detected in HI 21cm line using the Giant Meter-wave Radio Telescope (GMRT). The median blue band magnitude of our sample is ~ -11.6, which is more than one magnitude fainter than earlier FIGGS survey. From our GMRT observations we find that, for many of our sample galaxies, the HI disks are offset from their optical disks. The HI diameters of the FIGGS2 galaxies show a tight correlation with their HI mass. The slope of the correlation is 2.08 +/- 0.20 similar to what is found for FIGGS galaxies. We also find that for almost all galaxies, the HI disks are larger than the optical disks which is a common trend for dwarf or spiral galaxies. The mean value of the ratio of HI to optical diameter is ~ 1.54., Comment: 12 pages, 8 figures, accepted for publication in Astrophysical Bulletin

We report the discovery of DGSAT I, an ultra-diffuse, quenched galaxy located 10.4 degrees in projection from the Andromeda galaxy (M31). This low-surface brightness galaxy (mu_V = 24.8 mag/arcsec), found with a small amateur telescope, appears unresolved in sub-arcsecond archival Subaru/Suprime-Cam images, and hence has been missed by optical surveys relying on resolved star counts, in spite of its relatively large effective radius (R_e(V) = 12 arcsec) and proximity (15 arcmin) to the well-known dwarf spheroidal galaxy And II. Its red color (V-I = 1.0), shallow Sersic index (n_V=0.68), and the absence of detectable H-alpha emission are typical properties of dwarf spheroidal galaxies and suggest that it is mainly composed of old stars. Initially interpreted as an interesting case of an isolated dwarf spheroidal galaxy in the local universe, our radial velocity measurement obtained with the BTA 6-meter telescope (V_h=5450 +/- 40 km/s) shows that this system is an M31-background galaxy associated with the filament of the Pisces-Perseus supercluster. At the distance of this cluster (~78 Mpc), DGSAT I would have an R_e ~ 4.7 kpc and M_V ~-16.3$. Its properties resemble those of the ultra-diffuse galaxies recently discovered in the Coma cluster. DGSAT I is the first case of these rare ultra-diffuse galaxies found in this galaxy cluster. Unlike the ultra-diffuse galaxies associated with the Coma and Virgo clusters, DGSAT I is found in a much lower density environment, which provides a fresh constraint on the formation mechanisms for this intriguing class of galaxy., Comment: Accepted for publication in The Astronomical Journal. 18 pages, 8 figures, 2 Tables

We present the results of a study of the amount and distribution of cold atomic gas, as well its correlation with recent star formation in a sample of extremely faint dwarf irregular galaxies. Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) and its extension, FIGGS2. We use two different methods to identify cold atomic gas. In the first method, line-of-sight HI spectra were decomposed into multiple Gaussian components and narrow Gaussian components were identified as cold HI. In the second method, the brightness temperature (T_B) is used as a tracer of cold HI. We find that the amount of cold gas identified using the T_B method is significantly larger than the amount of gas identified using Gaussian decomposition. We also find that a large fraction of the cold gas identified using the T_B method is spatially coincident with regions of recent star formation, although the converse is not true. That is only a small fraction of the regions with recent star formation are also covered by cold gas. For regions where the star formation and the cold gas overlap, we study the relationship between the star formation rate density and the cold \HI column density. We find that the star formation rate density has a power law dependence on the HI column density, but that the slope of this power law is significantly flatter than that of the canonical Kennicutt-Schmidt relation., Comment: Accepted for publication in MNRAS

Tip of the red giant branch measurements based on Hubble Space Telescope and ground-based imaging have resulted in accurate distances to 29 galaxies in the nearby Centaurus A Group. All but two of the 29 galaxies lie in either of two thin planes roughly parallel with the supergalactic equator. The planes are only slightly tilted from the line-of-sight, leaving little ambiguity regarding the morphology of the structure. The planes have characteristic r.m.s. long axis dimensions of ~300 kpc and short axis dimensions of ~60 kpc, hence axial ratios ~0.2, and are separated in the short axis direction by 303 kpc., Comment: Accepted for publication in Astrophysical Journal Letters

In the region of the sky limited by the coordinates RA$=7.0^h...12.0^h$, Dec$=0^\circ...+20^\circ$ and extending from the Virgo Cluster to the South Pole of the Local Supercluster, we consider the data on the galaxies with radial velocities $V_{LG}\lesssim 2000$ km/s. For 290 among them, we determine individual distances and peculiar velocities. In this region, known as the local velocity anomaly zone, there are 23 groups and 20 pairs of galaxies for which the estimates of virial/orbital masses are obtained. A nearby group around NGC3379 = Leo I and NGC3627 as well as the Local Group show the motion from the Local Void in the direction of Leo cloud with a characteristic velocity of about 400 km/s. Another rich group of galaxies around NGC3607 reveals peculiar velocity of about -420 km/s in the frame of reference related with the cosmic background radiation. A peculiar scattered association of dwarf galaxies Gemini Flock at a distance of 8 Mpc has the radial velocity dispersion of only 20 km/s and the size of approximately 0.7 Mpc. The virial mass estimate for it is 300 times greater than the total stellar mass. The ratio of the sum of virial masses of groups and pairs in the Leo/Can region to the sum of stellar masses of the galaxies contained in them equals 26, which is equivalent to the local average density $\Omega_{m(local)} = 0.074$, which is 3-4 times smaller than the global average density of matter., Comment: 23 pages, 10 figures, 3 tables. Accepted to Astrophysical Bulletin

Bootes filament of galaxies is a dispersed chain of groups residing on sky between the Local Void and the Virgo cluster. We consider a sample of 361 galaxies inside the sky area of $RA = 13.0^h ... 18.5^h$ and $Dec = -5^\circ ... +10^\circ$ with radial velocities $V_{LG} < 2000$ km/s to clarify its structure and kinematics. In this region, 161 galaxies have individual distance estimates. We use these data to draw the Hubble relation for galaxy groups, pairs as well as the field galaxies, and to examine the galaxy distribution on peculiar velocities. Our analysis exposes the known Virgo-centric infall at $RA < 14^h$ and some signs of outflow from the Local Void at $RA > 17^h$. According to the galaxy grouping criterion, this complex contains the members of 13 groups, 11 pairs and 140 field galaxies. The most prominent group is dominated by NGC5846. The Bootes filament contains the total stellar mass of $2.7\times10^{12} M_\odot$ and the total virial mass of $9.07\times10^{13} M_\odot$, having the average density of dark matter to be $\Omega_m = 0.09$, i.e. a factor three lower than the global cosmic value., Comment: 3 pages, 3 figures. Submitted to the Proceedings of the IAU Symposium 308 (The Zeldovich Universe: Genesis and Growth of the Cosmic Web)

We use data for faint (M_B > -14.5) dwarf irregular galaxies drawn from the FIGGS survey to study the correlation between the atomic gas density (Sigma_gas,atomic) and star formation rate (Sigma_SFR) in the galaxies. The estimated gas phase metallicity of our sample galaxies is Z ~ 0.1 Z_sun. Understanding star formation in such molecule poor gas is of particular importance since it is likely to be of direct relevance to simulations of early galaxy formation. For about 20% (9/43) of our sample galaxies, we find that the HI distribution is significantly disturbed, with little correspondence between the optical and HI distributions. We exclude these galaxies from the comparison. We also exclude galaxies with very low star formation rates, for which stochastic effects make it difficult to estimate the true star formation rates. For the remaining galaxies we compute the Sigma_gas,atomic and Sigma_SFR averaged over the entire star forming disk of the galaxy. For these galaxies we find a nearly linear relation between the star formation rate and the atomic gas surface densities. The corresponding gas consumption timescale is ~ 10 Gyr, i.e. significantly smaller than the ~ 100 Gyr estimated for the outer regions of spiral galaxies. We also estimate the gas consumption timescale computed using the global gas content and the global star formation rate for all galaxies with a reliable measurement of the star formation rate, regardless of whether the HI distribution is disturbed or not. The mean gas consumption timescale computed using this entire gas reservoir is ~ 18 Gyr, i.e. still significantly smaller than that estimated for the outer parts of spirals. The gas consumption timescale for dwarfs is intermediate between the values of ~ 100 Gyr and ~ 2 Gyr estimated for the outer molecule poor and inner molecule rich regions of spiral disks., Comment: 11 pages (+1 as appendix), 10 Figures (+1 in appendix), 2 Tables. Accepted for publication in MNRAS Main Journal. For the definitive version visit http://mnras.oxfordjournals.org/

We explore the structure and kinematics of a dispersed filament of galaxies residing between the Local Void and the Virgo cluster. For such purpose, we consider a sample of 361 galaxies with radial velocities $V_{LG} < 2000$ km/s inside the sky area of RA = [13.0 ... 18.0]$^h$ and Dec. = [$-$5 ... $+$10]$^\circ$. At present, 161 of them have individual distance estimates. The galaxy distribution on peculiar velocities along the strip exhibits the known Virgo-centric infall at RA < 14$^h$ and some signs of outflow from the Local Void at RA > 17$^h$. Majority of the Bootes strip galaxies (56%) belong to 13 groups and 11 pairs, with the most prominent group around NGC5846. The Bootes strip groups reside within [17$-$27]Mpc, being all farther from us than the Virgo cluster. The Bootes filament contains the total stellar mass of $2.7\times10^{12} M_\odot$ and the total virial mass of $9.07\times10^{13} M_\odot$, having the average density of dark matter to be $\Omega_m = 0.09$, i.e. a factor three lower than the global cosmic average., Comment: 19 pages, 7 figures, 3 tables. Accepted by Astrofizika

We use observational properties of galaxies accumulated in the Updated Nearby Galaxy Catalog to derive a dark matter mass of luminous galaxies via motions of their companions. The data on orbital-to-stellar mass ratio are presented for 15 luminous galaxies situated within 11 Mpc from us: the Milky Way, M31, M81, NGC5128, IC342, NGC253, NGC4736, NGC5236, NGC6946, M101, NGC4258, NGC4594, NGC3115, NGC3627 and NGC3368, as well as for a composit suite around other nearby galaxies of moderate and low luminosity. The typical ratio for them is M_{orb}/M* = 31, corresponding to the mean local density of matter Omega_m = 0.09, i.e 1/3 of the global cosmic density. This quantity seems to be rather an upper limit of dark matter density, since the peripheric population of the suites may suffer from the presence of fictitious unbound members. We notice that the Milky Way and M31 haloes have lower dimensions and lower stellar masses than those of other 13 nearby luminous galaxies. However, the dark-to-stellar mass ratio for both the Milky Way and M31 is the typical one for other neighboring luminous galaxies. The distortion in the Hubble flow, observed around the Local Group and five other neighboring groups yields their total masses within the radius of zero velocity surface,R_0, which are slightly lower than the orbital and virial values. This difference may be due to the effect of dark energy, producing a kind of "mass defect" within R_0., Comment: 35 pages, 5 tables, 5 figures, accepted by AJ

In this paper, we extend the use of the tip of the red giant branch (TRGB) method to near-infrared wavelengths from previously-used $I$-band, using the \textit{Hubble Space Telescope (HST)} Wide Field Camera 3 (WFC3). Upon calibration of a color dependency of the TRGB magnitude, the IR TRGB yields a random uncertainty of $\sim 5%$ in relative distance. The IR TRGB methodology has an advantage over the previously-used ACS $F606W$ and $F814W$ filter set for galaxies that suffer from severe extinction. Using the IR TRGB methodology, we obtain distances toward three principal galaxies in the Maffei/IC 342 complex, which are located at low Galactic latitudes. New distance estimates using the TRGB method are 3.45$^{+0.13}_{-0.13}$ Mpc for IC 342, 3.37$^{+0.32}_{-0.23}$ Mpc for Maffei 1 and 3.52$^{+0.32}_{-0.30}$ Mpc for Maffei 2. The uncertainties are dominated by uncertain extinction, especially for Maffei 1 and Maffei 2. Our IR calibration demonstrates the viability of the TRGB methodology for observations with the \textit{James Webb Space Telescope (JWST)}., Comment: 14 pages, 14 figure, submitted to AJ

We report the discovery of three low surface brightness companions to the spiral galaxy NGC 4631, made with small amateur telescopes. Assuming their distances to be 7.4 Mpc, the same as that of NGC 4631, the absolute magnitudes and linear diameters of the dwarfs are ranged within [-12.5, -9.6] mag and [4.7 - 1.3] kpc, respectively. These new three dwarfs, together with the discovered by us diffuse structure called "bridge", look like parts of a tidal filament directed towards NGC 4656 at total extended over 100 kpc., Comment: 8 pages, 2 figures, 1 table

We measured the Tip of the Red Giant Branch distances to nine galaxies in the direction to the Virgo cluster using the Advanced Camera for Surveys on the Hubble Space Telescope. These distances put seven galaxies: GR 34, UGC 7512, NGC 4517, IC 3583, NGC 4600, VCC 2037 and KDG 215 in front of the Virgo, and two galaxies: IC 3023, KDG 177 likely inside the cluster. Distances and radial velocities of the galaxies situated between us and the Virgo core clearly exhibit the infall phenomenon toward the cluster. In the case of spherically symmetric radial infall we estimate the radius of the "zero-velocity surface" to be (7.2+-0.7) Mpc that yields the total mass of the Virgo cluster to be (8.0+-2.3) X 10^{14} M_sun in good agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark matter beyond its virial radius., Comment: 27 pages, 2 tables, 6 figures, accepted for publication in Astrophysical Journal

We consider a sample of the Updated Nearby Galaxy Catalog that contains eight hundred objects within 11 Mpc. Environment of each galaxy was characterized by a tidal index $\Theta_1$ depending on the separation and mass of the galaxy's Main Disturber (=MD). We ascribed the UNGC galaxies with a common MD to its suite, and ranked suite members according to their $\Theta_1$. All suite members with positive $\Theta_1$ are assumed to be physical companions of the MD. The distribution of suites by the number of members, n, follows to a relation $N(n) \sim n^{-2}$. The twenty most populated suites contain 468 galaxies, i.e. 59% of the UNGC sample. About 58% of our sample are members of physical groups. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at $M_B = -18^m$. We discuss various properties of MDs, as well as galaxies belonging to their suites. The suite abundance practically does not depend on morphological type, linear diameter or hydrogen mass of MD, revealing the tightest correlation with the MD dynamical mass. Dwarf galaxies around MDs exhibit well-known segregation effects: the members of outskirts have later morphological types, richer HI-contents and higher rates of star formation activity. Nevertheless, there are some intriguing cases when dwarf spheroidal galaxies occur at the far periphery of the suites, as well as some late-type dwarfs residing close to MDs. The multiplicity of nearby groups according to number of their physical members can be described by the Hirsh-like index $h_g = 9$, indicating that the Local Volume contains 9 groups with populations exceeding 9 members. (abridged), Comment: 5 tables, 7 figures. Accepted for The Astronomical Journal. The electronic version of tables as well as the article with figures in high resolution are available at the Local Volume Galaxies database web-page http://www.sao.ru/lv/lvgdb

We have followed up on the results of a 65 square degree CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M_r' = -10, we find a galaxy luminosity function slope of -1.27+-0.04 for the M81 group. In this region, there are now 36 M81 group members known, including 4 blue compact dwarfs, 8 other late types including the interacting giants M81, NGC 3077, and M82, 19 early type dwarfs, and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size R_e ~ 100 pc and total magnitude estimates M_r' = -6.8 and M_I ~ -9.1., Comment: 56 pages including 39 figures. To be published in AJ

We use the measured B band axial ratios of galaxies from an updated catalog of Local Volume galaxies to determine the intrinsic shape of dwarf irregular galaxies (de Vacouleurs' morphological types 8, 9 and 10). We find that the shapes change systematically with luminosity, with fainter galaxies being thicker. In particular, we divide our sample into sub-samples and find that the most luminous dwarfs (-19.6 < M_B < -14.8) have thin discs (thickness ~ 0.2), with the disc being slightly elliptical (axial ratio ~ 0.8). At intermediate luminosity, viz. -14.8 < M_B < -12.6, the galaxies are still characterized by elliptical discs (axial ratio ~ 0.7), but the discs are somewhat thicker (thickness ~ 0.4). The faintest dwarfs, viz. those with -12.6 < M_B < -6.7 are well described as being oblate spheroids with an axial ratio ~ 0.5. The increasing thickness of the stellar discs of dwarf irregulars with decreasing luminosity is compatible with the increasing ratio of velocity dispersion to rotational velocity with decreasing galaxy size., Comment: 5 pages, 6 figures, 2 tables. Accepted for publication in MNRAS Letters. For the definitive version visit http://mnrasl.oxfordjournals.org/

Cosmicflows-2 is a compilation of distances and peculiar velocities for over 8000 galaxies. Numerically the largest contributions come from the luminosity-linewidth correlation for spirals, the TFR, and the related Fundamental Plane relation for E/S0 systems, but over 1000 distances are contributed by methods that provide more accurate individual distances: Cepheid, Tip of the Red Giant Branch, Surface Brightness Fluctuation, SNIa, and several miscellaneous but accurate procedures. Our collaboration is making important contributions to two of these inputs: Tip of the Red Giant Branch and TFR. A large body of new distance material is presented. In addition, an effort is made to assure that all the contributions, our own and those from the literature, are on the same scale. Overall, the distances are found to be compatible with a Hubble Constant H_0 = 74.4 +-3.0 km/s/Mpc. The great interest going forward with this data set will be with velocity field studies. Cosmicflows-2 is characterized by a great density and high accuracy of distance measures locally, falling to sparse and coarse sampling extending to z=0.1., Comment: To be published in Astronomical Journal. Two extensive tables to be available on-line. Table 1 available at http://edd.ifa.hawaii.edu select catalog `Cosmicflows-2 Distances'

A distance-limited sample of 869 objects from the Updated Nearby Galaxy Catalog is used to characterize the star formation status of the Local Volume population. We present a compiled list of 1217 star formation rate (SFR) estimates for 802 galaxies within 11 Mpc from us, derived from the H-alpha imaging surveys and GALEX far-ultraviolet survey. We briefly discuss some basic scaling relations between SFR and luminosity, morphology, HI-mass, surface brightness, as well as environment of the galaxies. About 3/4 of our sample consist of dwarf galaxies, for which we offer a more refined classification. We note that the specific star formation rate of nearly all luminous and dwarf galaxies does not exceed the maximum value: $\log(SFR/L_K) = -9.4$ [yr$^{-1}$]. The bulk of spiral and blue dwarf galaxies have enough time to generate their stellar mass during the cosmological time, $T_0$, with the observed SFRs. They dispose of a sufficient amount of gas to support their present SFRs over the next $T_0$ term. We note that only a minor part of BCD, Im, and Ir galaxies (about 1/20) proceeds in a mode of vigorous star-burst activity. In general, the star formation history of spiral and blue dwarf galaxies is mainly driven by their internal processes. The present SFRs of E, S0 and dSph galaxies are typically (1/30 - 1/300) of their former activity., Comment: 4 tables, 8 figures. The electronic version of tables as well as the article with figures in high resolution are available at the Local Volume Galaxies database web-page http://www.sao.ru/lv/lvgdb/. Accepted for The Astronomical Journal

We present an all-sky catalog of 869 nearby galaxies, having individual distance estimates within 11 Mpc or corrected radial velocities V_{LG} < 600 km/s. The catalog is a renewed and expanded version of the "Catalog of Neighboring Galaxies" by Karachentsev et al. (2004). It collects data on the following observables for the galaxies: angular diameters, apparent magnitudes in FUV-, B-, and K_s- bands, H_alpha and HI fluxes, morphological types, HI-line widths, radial velocities and distance estimates. In this Local Volume (LV) sample 108 dwarf galaxies remain to be still without measured radial velocities. The catalog yields also calculated global galaxy parameters: linear Holmberg diameter, absolute B-magnitude, surface brightness, HI-mass, stellar mass estimated via K-band luminosity, HI rotational velocity corrected for galaxy inclination, indicative mass within the Holmberg radius, and three kinds of "tidal index", which quantify the local density environment. The catalog is supplemented with the data based on the local galaxies (http://www.sao.ru/lv/lvgdb), which presents their optical and available H_alpha images, as well as other service. We briefly discuss the Hubble flow within the LV, and different scaling relations that characterize galaxy structure and global star formation in them. We also trace the behavior of the mean stellar mass density, HI-mass density and star formation rate density within the considered volume., Comment: 6 tables, 20 figures. The electronic version of tables as well as the article with figures in high resolution are available at the Local Volume Galaxies database web-page http://www.sao.ru/lv/lvgdb/

We collected data on radial velocities and distances of galaxies to elucidate structure and kinematics of the filament attached to the Virgo cluster from south. In the region RA = [12.5 - 13.5]h, Dec = [-20 - 0]deg there are 171 galaxies with radial velocities VLG < 2000 km/s, and 98 of them have distance estimates. This galaxy cloud, called as "Virgo Southern Extension", is situated just on the edge of the Virgo "zero-velocity surface". The mean distance to Virgo SEx, 17pm2 Mpc, and the average radial velocity, 1172pm23 km/s, are very close to the Virgo cluster ones. In Supergalactic coordinates the Virgo SEx dimensions are 15x7x2 Mpc, where the major axis is directed along the line of sight, the second-major axis looks towards the Virgo core and the minor one is perpendicular to the Supergalactic plane. This flattened cloud consists of a dozen virialized groups with the total K-band luminosity of 1.7cdot10^12 Lsol and the total virial mass of 6.3cdot10^13 Msol, having a typical dark matter-to-stellar matter ratio of 37. The Hubble diagram for Virgo SEx galaxies exhibits a tendency of Z-shape wave with a velocity amplitude of ~250 km/s that may be caused by a mass overdensity of ~6cdot10^13 Msol, and in order of magnitude agrees with the sum of virial masses of the groups., Comment: 19 pages, 4 figures, 2 tables, accepted for MNRAS, Dec 4, 2012

We present the results from a search for HI emission from a sample of newly discovered dwarf galaxies in the M81 group. HI is detected in three galaxies, all of which are classified as BCDs. The HI masses of these galaxies are ~ 10^6 M_sun, making these some of the lowest mass BCDs known. For these three galaxies FUV images (from GALEX) and H-alpha images (from the Russian 6m BTA telescope) are available.The H-alpha emission is very faint, and, in principle could be produced by a single O star. Further, in all cases we find offsets between the peak of the FUV emission and that of the H-alpha emission. Offsets between the most recent sites of star formation (i.e. those traced by H-alpha) and the older sites (i.e. those traced by FUV) would be natural if the star formation is stochastic. In spite of the expectation that the effects of mechanical feedback from star formation would be most directly seen in the smallest galaxies with low gravitational potentials, we only see tentative evidence of outflowing HI gas associated with the star forming region in one of the galaxies., Comment: 9 pages, 5 figures, 5 tables. Accepted for publication in MNRAS. The definitive version is available at www.blackwell-synergy.com

We notice that nearby galaxies having high negative peculiar velocities are distributed over the sky very inhomogeneously. A part of this anisotropy is caused by the "Local Velocity Anomaly", i.e. by the bulk motion of nearby galaxies away from the Local Void. But a half of the fast-flying objects reside within a small region RA = [11.5h, 13.0h], Dec. = [+20\circ, +40\circ], known as the Coma I cloud. According to Makarov & Karachentsev (2011), this complex contains 8 groups, 5 triplets, 10 pairs and 83 single galaxies with the total mass of 4.7\star10^13M\odot. We use 122 galaxies in the Coma I region with known distances and radial velocities VLG < 3000 km/s to draw the Hubble relation for them. The Hubble diagram shows a Z-shape effect of infall with an amplitude of +200 km/s on the nearby side and -700 km/s on the back side. This phenomena can be understood as the galaxy infall towards a dark attractor with the mass of \sim 2\star10^14M\odot situated at a distance of 15 Mpc from us. The existence of large void between the Coma and Virgo clusters affects probably the Hubble flow around the Coma I also., Comment: Accepted for publication in ApJ, 23 pages, 4 figures

Aims. This work aims to provide a new mass estimate for the Fornax cluster and the Fornax-Eridanus complex, avoiding methods like the virial or fits of X-ray emission profile, which assume that the system is in equilibrium, probably not the case of Fornax, still in process of formation. Methods. Our mass estimate is based on the determination of the zero-velocity surface which, in the context of the spherical infall model permits an evaluation of the total mass inside such a surface. The zero-velocity surface radius R0 was estimated either by a running median procedure or by fitting the data to the velocity field expected from the spherical model, including effects of the cosmological constant. The velocity field in a region within 20 Mpc of the Fornax center was mapped using a list of 109 galaxies whose distances have an average accuracy of 0.31 mag in their distance modulus. Results. Our analysis indicates that the mass of the Fornax cluster itself inside a radius of [2.62-5.18] Mpc is [0.40-3.32] \times 10^14 Modotwhile the mass inside [3.88-5.60] Mpc, corresponding to the Fornax-Eridanus complex is [1.30-3.93] \times 10^14 M\odot., Comment: Version 1. 13 pages, 10 figures, 5 tables. Accepted to Astronomy & Astrophysics

We study the relationship between the gas column density (Sigma_HI) and the star formation rate surface density (Sigma_SFR) for a sample of extremely small (M_B ~ -13, Delta V_50 ~ 30 km/s) dwarf irregular galaxies. We find a clear stochasticity in the relation between the gas column density and star formation. All gas with Sigma_HI >~ 10 M_sun/pc^2 has some ongoing star formation, but the fraction of gas with ongoing star formation decreases as the gas column density decreases, and falls to about 50% at Sigma_HI ~ 3 M_sun/pc^2. Further, even for the most dense gas, the star formation efficiency is at least a factor of ~ 2 smaller than typical of star forming regions in spirals. We also find that the ratio of H-alpha emission to FUV emission increases with increasing gas column density. This is unlikely to be due to increasing dust extinction because the required dust to gas ratios are too high. We suggest instead that this correlation arises because massive (i.e. H-alpha producing) stars are formed preferentially in regions with high gas density., Comment: 5 pages, 5 figures, 1 table. Accepted for publication in MNRAS Letters. The definitive version is available at www.blackwell- synergy.com

We compare the cumulative star formation histories (SFHs) of Local Group (LG) dwarf galaxies with those in the volume-limited ACS Nearby Galaxy Survey Treasury (ANGST) sample (D < 4 Mpc), in order to understand how typical the LG dwarf galaxies are relative to those in the nearby universe. The SFHs were derived in a uniform manner from high quality optical color-magnitude diagrams constructed from Hubble Space Telescope imaging. We find that the {\it mean} cumulative SFHs of the LG dwarfs are comparable to the mean cumulative SFHs of the ANGST sample for the three different morphological types (dwarf spheroidals/ellipticals: dSph/dE; dwarf irregulars: dI; transition dwarfs: dTrans). We also discuss effects such as population gradients and systematic uncertainties in the stellar models that may influence the derived SFHs. Both the ANGST and Local Group dwarf galaxies show a consistent and strong morphology-density relationship, emphasizing the importance of environment in the evolution of dwarf galaxies. Specifically, we confirm that dIs are found at lower densities and higher luminosities than dSphs, within this large sample. We also find that dTrans are located in similar environments to those occupied by dwarf irregular galaxies, but have systematically lower luminosities that are more comparable to those of dwarf spheroidals. The similarity of the SFHs and morphology-density relationships of the LG and ANGST dwarf galaxies suggests that the LG dwarfs are a good representation of dwarf galaxies in the local universe., Comment: 10 pages, 4 figures. Accepted to ApJ

We present uniformly measured star formation histories (SFHs) of 60 nearby (D~4Mpc) dwarf galaxies based on CMDs of resolved stellar populations from images taken with HST as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dSph/dE, 5 dwarf spiral, 28 dI, 12 transition, and 3 tidal dwarf galaxies. From the best fit SFHs we find three significant results: (1) the average dwarf galaxy formed >50% of its stars by z~2 and 60% of its stars by z~1, regardless of current morphological type; (2) the mean SFHs of dIs, dTrans, and dSphs are similar over most of cosmic time, with the clearest differences appearing during the most recent 1 Gyr; and (3) the mean values are inconsistent with simple SFH models, e.g., exponentially declining SFRs. The mean SFHs are in general agreement with the cosmic SFH, although we observe offsets near z~1 that could be evidence that low mass systems experienced delayed star formation relative to more massive galaxies. The sample shows a strong density-morphology relationship, such that the dSphs are less isolated than dIs. We find that the transition from a gas-rich to gas-poor galaxy cannot be solely due to internal mechanisms such as stellar feedback, and instead is likely the result of external mechanisms, e.g., ram pressure and tidal forces. The average transition dwarf is slightly less isolated and less gas-rich than the typical dI. Further, the transition dwarfs can be divided into two groups: interacting and gas-poor or isolated and gas-rich, suggesting two possible evolutionary pathways., Comment: Submitted to ApJ; 32 pages, 16 Figures

We have carried out an H-alpha flux measurement for 52 nearby galaxies as part of a general H-alpha imaging survey for the Local Volume sample of galaxies within 10 Mpc. Most of the objects are probable members of the groups around Maffei 2/IC 342, NGC 672/IC 1727, NGC 784, and the Orion galaxy. The measured H-alpha fluxes corrected for extinction are used to derive the galaxy star formation rate (SFR). We briefly discuss some basic scaling relations between SFR, hydrogen mass and absolute magnitude of the Local Volume galaxies. The total SFR density in the local (z = 0) universe is estimated to be (0.019+/-0.003) M_sun yr/Mpc^3., Comment: 29 pages, 6 figures, 7 tables (figures 2 and 3 is available at this this http://una.sao.ru/halpha/articles/Maffield),Astronomical Journal, accepted

Recent observations of UGC4879 with the Advanced Camera for Surveys on the Hubble Space Telescope confirm that it is a nearby isolated dwarf irregular galaxy. We measure a distance of 1.36+/-0.03 Mpc using the Tip of the Red Giant Branch method. This distance puts UGC4879 beyond the radius of first turnaround of the Local Group and ~700 kpc from its nearest neighbor Leo A. This isolation makes this galaxy an ideal laboratory for studying pristine star formation uncomplicated by interactions with other galaxies. We present the star formation history of UGC4879 derived from simulated color-magnitude diagrams., Comment: 10 pages, 15 figures. Accepted for publication in the Astronomical Journal