ABSTRACT
We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° ...hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ M}_\odot$, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10−5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.
ABSTRACT
We present the results of a narrow-band Hα and S ii imaging survey of the Mon R1 association performed with the 1-m Schmidt telescope at Byurakan Observatory. Our observations covered a 1° ...field near the centre of the association. As a result of this study, 20 new Herbig–Haro knots were discovered, some of which form collimated outflows. Among the most extended ones are HH 1203 and HH 1196, which have a length of 1 pc or even more. During the search for the probable sources of HH objects, several new nebulous stars were found. A list of all nebulous stellar objects in the Mon R1 area under study is presented, with detailed descriptions of the most interesting ones. The near-infrared data from the GLIMPSE360 and WISE surveys revealed several more objects related to Mon R1, some of which had optical counterparts, as well as helped to identify at least three probable H2 collimated flows from the deeply embedded pre-main-sequence objects. The probable members of Mon R1 were selected by their distances; their bolometric luminosities and extinctions were estimated. Among the outflow sources, three embedded objects with luminosities greater than 10 L⊙ were found. The mean distance to the Mon R1 complex is estimated as 715 pc.
ABSTRACT
We present the gMOSS (Galaxies of Medium-band One-meter Schmidt telescope Survey) catalogue of ∼19 000 galaxies in 20 filters (4 broad-band SDSS and 16 medium-band filters). We observed ...2.386 deg2 on the central part of the HS47.5-22 field with the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory. The gMOSS is a complete flux-limited sample of galaxies with a threshold magnitude of r SDSS ≤ 22.5 AB. From photometric measurements with 16 medium-band filters and u SDSS, we get spectral energy distributions for each object in the field, which are used for further analysis. Galaxy classification and photometric redshift estimation based on spectral template matching with zebra software. The obtained redshift accuracy is σNMAD < 0.0043. Using the SED-fitting cigale code, we obtained the main properties of the stellar population of galaxies, such as rest-frame (u − r)res colour, stellar mass, extinction, and mass-weighted age with a precision of 0.16 ± 0.07 mag, 0.14 ± 0.04 dex, 0.27 ± 0.1 mag, and 0.08 ± 0.04 dex, respectively. Using a dust-corrected colour–mass diagram, we divided the full sample into populations of red and blue galaxies and considered the dependencies between stellar mass and age. Throughout cosmic time, red sequence galaxies remain older and more massive than blue cloud galaxies. The star formation history of a complete subsample of galaxies selected in the redshift range 0.05 ≤ z ≤ 0.015 with <$\mathrm{log} M \mathrm{\gt }_\mathrm{M_\odot }$>8.3 shows an increase in the SFRD up to z ∼ 3, under the results obtained in earlier studies.
The galaxy SBS1001+555 is studied as an object from the base sample in our program for study of evolutionary processes of star formation in galaxies. The work is based on the results of panoramic ...spectroscopy of the central part, which is the activity zone of the galaxy with its main star formation region, which we denote by A. The observations employ an MPFS (multipupil fiber spectrograph) on the 6-m telescope of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS) to yield a 635-725 nm spectral band with a dispersion of 0.76 Å/pixel. Besides the most intense Balmer Hα emission line, the resulting integrated spectrum includes the HeI 6678 and HeI 7065 lines, forbidden lines of nitrogen, sulfur, and argon, NII 6548, 6583, SII 6716, 6731, and ArIII 7136 Å, and more than ten faint lines of neutral and singly ionized iron and neon, FeI 6824, 6837, 7447, 7453, and 7544, NeI 7245 and 7544, FeII 7682 and 7687, and NeII 7213 Å. A detailed analysis is made of the twodimensional distributions of the intensities, radial velocities, and other parameters over the field of view in Hα. Besides A, the largest and brightest HII region, three small regions A1, A2, and A3 have been identified, which form a common structure with A. One of the secondary regions, A1, is revealed with a condensation that stands out in an IRAC 4.5 μm image. The values of the main parameters in their peaks are taken to be the numerical characteristics of the HII regions, and those of the integral formations are taken to be the equivalent radius, luminosity, and star-formation rate, Req, L(Hα), and SFR(Hα). The data shown here, in particular, are indicative of active processes immediately associated with the brightest source of visible radiation in SBS1001+555 and the development of a star-formation structure around it.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Based on a medium-band photometric survey at the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory, we have produced a complete sample of quasars to 22.5 mag in the HS47.5-22 field with ...an area of 2.38 deg
. We have classified the objects and produced the sample of quasars using broadband photometric data and the morphological classification from DECaLS (Dey et al. 2019), infrared photometry from WISE (Meisner et al. 2018), spectroscopy from SDSS (Pâris et al. 2018), ROSAT X-ray data (Molthagen et al. 1997), FIRST radio data (Becker et al. 1995), and data on the proper motions of objects from the Gaia survey (Brown et al. 2018). The sample contains 682 quasars for which we have determined the medium-band photometric redshifts, calculated the absolute magnitudes, and investigated the quasar space density distribution and luminosity function. As a result, we have obtained evidence for the absence of a significant reduction in the space density of quasars up to
.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present the results of optical identifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources (PSZ2) located at high ...redshifts,
z
≈ 0.7−0.9. We used the data of optical observations with the Russian–Turkish 1.5-mtelescope (RTT-150), the Sayan Observatory 1.6-m telescope, the Calar Alto 3.5-m telescope, and the 6-m SAO RAS telescope (BTA). The spectroscopic redshift measurements were obtained for seven galaxy clusters, including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of the PSZ2 catalogue. In the central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2 G087.39−34.58, we detected arcs of strong gravitational lensing of background galaxies, one of which is at redshift
z
= 4.262. The data presented below roughly double the number of known galaxy clusters in the second Planck catalogue of Sunyaev–Zeldovich sources at high redshifts,
z
≈ 0.8.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present the results of the optical identification and spectroscopic redshift measurements of 216 galaxy clusters detected in the SRG/eROSITA all-sky X-ray survey. The spectroscopic observations ...were performed in 2020–2023 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences, the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University, the 1.6-m AZT-33IK telescope at the Sayan Solar Observatory of the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences, and the 1.5-m Russian–Turkish telescope (RTT-150) at the TÜBİTAK Observatory. For all of the galaxy clusters presented here the spectroscopic redshift measurements have been obtained for the first time. Of these, 139 galaxy clusters have been detected for the first time in the SRG/eROSITA survey and 22 galaxy clusters are at redshifts
, including three at
. Deep direct images with the
rizJK
filters have also been obtained for four distant galaxy clusters at
. For these observations we chose the most massive clusters and, therefore, most of the galaxy clusters presented here with the spectroscopic redshifts measured by us will most likely enter in future into the cosmological samples of galaxy clusters from the SRG/eROSITA survey.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Spectroscopic observations of 63 H ii regions in six spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 7331 and NGC 7678) were carried out with the 6-m telescope (BTA) of Russian ...Special Astrophysical Observatory with the Spectral Camera attached to the focal reducer SCORPIO in multislit mode with a dispersion of 2.1 Å pixel−1 and a spectral resolution of 10 Å. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in H ii regions through the recent variant of the strong-line method (NS calibration). The parameters of the radial distribution (the extrapolated central intercept value and the gradient) of the oxygen and nitrogen abundances in the discs of spiral galaxies NGC 628, NGC 783, NGC 2336, NGC 7331 and NGC 7678 have been determined. The abundances in NGC 783, NGC 2336, NGC 6217 and NGC 7678 are measured for the first time. Galaxies from our sample follow well the general trend in the luminosity-central metallicity diagram for spiral and irregular galaxies.
We present the results of our search for massive galaxy clusters among extended X-ray sources from the SRG/eROSITA survey using data from the Planck survey and data from optical and infrared sky ...surveys. Optical observations of these clusters are carried out with the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences (BTA), the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University (AZT-33IK), and the 1.5-m Russian–Turkish telescope (RTT-150). We provide data on the optical identifications and spectroscopic redshift measurements for 11 massive galaxy clusters with masses higher than
located at redshifts
–
. Such clusters are very rare objects; most of the clusters with such a high mass in the observable Universe have already been detected previously by the Sunyaev–Zeldovich effect in the Planck all-sky survey. Being anomalous, they can be sensitive indicators of possible deviations of the cosmology from the standard
model with a quasi-flat spectrum of initial Gaussian perturbations.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
SRGe CL2305.2–2248 (SPT-CL J2305–2248, ACT-CL J2305.1–2248) is one of the most massive galaxy clusters at high redshifts (
) and is of great interest for cosmology. Deep images have been obtained at ...the Russian–Turkish 1.5-m telescope (RTT-150) for an optical identification of this cluster. In combination with the open Hubble Space Telescope archival data, they have made it possible to select candidates for gravitationally lensed images of distant blue galaxies in the form of arcs and arclets. The observed giant arc near the brightest cluster galaxies allows the Einstein radius to be estimated,
arcsec. The photometric redshift of the lensed source has been found (
). Its use in combination with the Einstein radius estimate has made it possible to independently estimate the mass of SRGe CL2305.2–2248 by extrapolating the strong-lensing results to large radii and using model density profiles in relaxed clusters. This extrapolation leads to mass estimates smaller than those obtained from X-ray and microwave observations by a factor of
. A probable cause of this discrepancy may be the galaxy merger process, which is also confirmed by the morphology of SRGe CL2305.2–2248 in the optical range.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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