arXiv subjects

Serafim Kaisin

Publications and source records attributed to Serafim Kaisin.

6 recordsLinked to original sources

arXiv2026

New optical velocities for local galaxy candidates

We used the 6-meter BTA telescope to determine radial velocities for 46 galaxies, previously considered to be nearby objects. Twelve of them have kinematic distances within 13Mpc and are new probable companions to the bright Local Volume galaxies: NGC1068, NGC2903, NGC4517, NGC4565, NGC4826. We also found a new tiny satellite of the nearby (10.38Mpc) SMC-like dwarf galaxy DDO46. Two isolated dIrr galaxies: dw1408-0802 and Dw1552-1027 are probably located inside the Local Void. The spectrum of the latter shows a rich set of emission lines. Using the radial velocities and projected separations of 13 NGC1068 satellites, we estimated the total mass of the group to be $M= (2.6\pm1.0)\times10^{12}\, M_\odot$.

astro-ph.GA↗

arXiv2017

First Characterization of the Neutral ISM in Two Local Volume Dwarf Galaxies

We present the first HI spectral line images of the nearby, star-forming dwarf galaxies UGC11411 and UGC 8245, acquired as part of the "Observing for University Classes" program with the Karl G. Jansky Very Large Array (VLA). These low-resolution images localize the HI gas and reveal the bulk kinematics of each system. Comparing with HST broadband and ground-based Hα imaging, we find that the ongoing star formation in each galaxy is associated with the highest HI mass surface density regions. UGC 8245 has a much lower current star formation rate than UGC 11411, which harbors very high surface brightness Hα emission in the inner disk and diffuse, lower surface brightness nebular gas that extends well beyond the stellar disk as traced by HST. We measure the dynamical masses of each galaxy and find that the halo of UGC 11411 is more than an order of magnitude more massive than the halo of UGC 8245, even though the HI and stellar masses of the sources are similar. We show that UGC8245 shares similar physical properties with other well-studied low-mass galaxies, while UGC11411 is more highly dark matter dominated. Both systems have negative peculiar velocities that are associated with a coherent flow of nearby galaxies at high supergalactic latitude.

astro-ph.GA↗

arXiv2016

Discovery of an ultra-diffuse galaxy in the Pisces-Perseus supercluster

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.

astro-ph.GA↗

arXiv2011

Emission sparks around M 81 and in some dSph galaxies

We use H-alpha images of three clumps of young stars situated between M81 and NGC3077 to estimate their star formation rate. Radial velocities of the clumps measured by us, as well as the velocity of HII-region in the dSph galaxy KDG61 are compatible with their location at the outskirts of a large rotating gaseous disc around M81. In contrast to KDG61, radial velocity of the emission knot in the dSph galaxy DDO44, +213+-25 km/s, tells us that this H-alpha spark belongs to the dSph galaxy itself. F475W and F814W images of DDO44 extracted from the HST archive reveal 8 bluish (B-I < 0.8) stars apparently associated with the H-alpha knot.

astro-ph.CO↗

arXiv2010

Ionized gas outflow in the isolated S0 galaxy NGC 4460

We use integral-field and long-slit spectroscopy to study the bright extended nebulosity discovered in the isolated lenticular galaxy NGC 4460 during a recent H-alpha survey of nearby galaxies. An analysis of archival SDSS, GALEX, and HST images indicates that current star formation is entirely concentrated in the central kiloparsec of the galaxy disc. The observed ionized gas parameters (morphology, kinematics and ionization state) can be explained by a gas outflow above the plane of the galaxy caused by a star formation in the circumnuclear region. Galactic wind parameters in NGC 4460: outflow velocity, total kinetic energy - are several times smaller comparing with the known galactic wind in NGC 253, which is explained substantially lower total star formation rate. We discuss the cause of the star formation processes in NGC 4460 and in two other known isolated S0 and E galaxies of the Local volume: NGC 404 and NGC 855. We provide evidence suggesting that feeding of isolated galaxies by intergalactic gas on a cosmological time scale is a steady process without significant variations.

astro-ph.CO↗

arXiv2007

Mining the Local Volume

After recent systematic optical, IR, and HI surveys, the total number of known galaxies within 10 Mpc has increased from 179 to 550. About half this Local Volume (LV) sample is now been imaged with HST, yielding the galaxy distances with an accuracy of about 8%. For the majority of the LV galaxies we currently have H-alpha fluxes that allow us to reconstruct the star formation history of our neighbourhood. For the late-type LV galaxies their HI masses and angular momentum follow the linear relation in the range of 4 orders, which is expected for rotating gaseous disks being near the gravitational instability threshold. The data obtained on the LV galaxies imply important cosmological parameters, in particular, the mean local matter density and HI mass density, as well as SFR density. Surprisingly, the local Hubble flow around the LV groups is very quiet, with 1D rms deviations of 25 km/s,which is a signature of the Universe vacuum-dominated on small scales. The cold infall pattern around nearby groups provides us with a new method to determine the total mass of the groups independent from virial mass estimates.

astro-ph↗