- ID:
- ivo://CDS.VizieR/J/ApJ/900/L34
- Title:
- BL Lac objects and radio galaxies comparison
- Short Name:
- J/ApJ/900/L34
- Date:
- 15 Feb 2022 00:20:41
- Publisher:
- CDS
- Description:
- The most elusive and extreme subclass of active galactic nuclei (AGNs), known as BL Lac objects, shows features that can only be explained as the result of relativistic effects occurring in jets pointing at a small angle with respect to the line of sight. A longstanding issue is the identification of the BL Lac parent population with jets oriented at larger angles. According to the "unification scenario" of AGNs, radio galaxies with low luminosity and an edge-darkened radio morphology are the most promising candidate parent population of BL Lacs. Here we compare the large-scale environment, an orientation-independent property, of well-defined samples of BL Lacs with samples of radio galaxies all lying in the local universe. Our study reveals that BL Lacs and radio galaxies live in significantly different environments, challenging predictions of the unification scenario. We propose a solution to this problem proving that large-scale environments of BL Lacs are statistically consistent with those of compact radio sources, known as FR 0s, and share similar properties. This implies that highly relativistic jets are ubiquitous and are the natural outcome of the accretion of gas into the deep gravitational potential well produced by supermassive black holes.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/600/A65
- Title:
- B2 0924+30 LOFAR HBA and WSRT maps
- Short Name:
- J/A+A/600/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using LOFAR (LOw Frequency ARray), Westerbork telescope and survey data, we map the spectral index and age of the remnant radio galaxy by using different ageing models.
- ID:
- ivo://CDS.VizieR/J/A+A/373/24
- Title:
- Blue compact galaxies from SBS
- Short Name:
- J/A+A/373/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The work studies of the environment of low-mass galaxies with active star formation (SF) and a possible trigger of SF bursts due to gravitational interaction. Following the study by Taylor et al. (1995ApJS...99..427T), we extend the search for possible disturbing galaxies of various masses to a much larger sample of 86 BCGs from the sky region of the Second Byurakan survey (SBS). The BCG magnitudes and radial velocities are revised and up-dated. The sample under study is separated by the criteria: EW([O III]5007)>45{AA} and V_h_<6000km/s nd should be representative of all low-mass galaxies which experience SF bursts.
- ID:
- ivo://CDS.VizieR/J/other/RAA/19.81
- Title:
- Blue-core galaxies properties
- Short Name:
- J/other/RAA/19.8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We select 107 blue-core galaxies from the MaNGA survey, studying their morphology, kinematics as well as the gas-phase metallicity. Our results are as follows: (i) In our sample, 26% of blue-core galaxies have decoupled gas-star kinematics, indicating external gas accretion; 15% have bar-like structure and 8% show post-merger features, such as tidal tails and irregular gas/star velocity field. All these processes/features, such as accreting external misaligned gas, interaction and bar, can trigger gas inflow. Thus the central star-forming activities lead to bluer colors in their centers (blue-core galaxies). (ii) By comparing with the SDSS DR7 star-forming galaxy sample, we find that the blue-core galaxies have higher central gas-phase metallicity than what is predicted by the local mass-metallicity relation. We explore the origin of the higher metallicity, finding that not only the blue-core galaxies, but also the flat-gradient and red-core galaxies all have higher metallicity. This can be explained by the combined effect of redshift and galaxy color.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/3977
- Title:
- Blue diffuse dwarf galaxies
- Short Name:
- J/MNRAS/465/3977
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ~150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43<12+log(O/H)<8.01), with ~20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ~1-33x10^-2^M_{sun}_/yr in HII regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M_*_/M_{sun}_)~=5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/2687
- Title:
- Blue diffuse dwarf galaxies spectroscopic data
- Short Name:
- J/MNRAS/448/2687
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45<12+log(O/H)<8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (<10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11<~M_B_<~-18) and low surface brightnesses (~23-25 mag/arcsec^2^), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078 M_{sun}_/yr. From our current subsample, BDD galaxies appear to be a population of non-quiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor star-forming galaxies, which traditional emission-line-based searches overlook.
- ID:
- ivo://CDS.VizieR/J/MNRAS/396/818
- Title:
- Blue early-type galaxies in Galaxy Zoo
- Short Name:
- J/MNRAS/396/818
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5<SFR<50M_{sun}_/yr). They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital Sky Survey Data Release 6 and their u-r colour. We select a volume-limited sample in the redshift range 0.02<z<0.05, corresponding to luminosities of approximately L* and above and with u-r colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties.
- ID:
- ivo://CDS.VizieR/J/A+AS/140/309
- Title:
- Blue-H{alpha} objects in M33
- Short Name:
- J/A+AS/140/309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the purposes of a search for SS433 type objects, LBV stars and hypergiants in M33, we have carried out a photometry of blue stars in H{alpha} images of this galaxy. From 2332 listed OB stars, we have isolated 549 objects, which have H{alpha} excess over stars of the same V magnitude. Among them 81 emission stars (s) have been selected. About 60% of isolated objects found to be extended in H{alpha}, among them 154 diffuse (d) and 180 bubble-type (b) nebulae. 117 objects are compact (c) and faint H{alpha} sources. These groups are different in colour indices, H{alpha} fluxes, surface brightness and sizes. The most probable size of the H{alpha} nebulae is FWHM=10-14pc. There is evidence that their properties and location in the galaxy are defined by interstellar gas pressure and related to spiral arms. The d objects are HII regions with an embedded star. The b objects are probably envelopes around WR stars or SN remnants. Among s-type objects we isolated a group of 20 brightest stars, which in their average properties fit well to the parameters of blue hypergiants or LBV-type stars. The stars of intermediate brightness follow very well to blue Ia supergiants. The interstellar absorption derived from brightest H{alpha} stars is A_V_=0.93+/-0.05mag. We classify the faintest stars as blue Ib supergiants, their average absorption is A_V_~0.6mag. They are restricted in number by the limiting stellar magnitude in the original sample.
- ID:
- ivo://CDS.VizieR/J/AJ/130/381
- Title:
- Blueshifted [O III] emission
- Short Name:
- J/AJ/130/381
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The [OIII]{lambda}5007 line is commonly used as an indicator of the systemic redshift of active galactic nuclei (AGNs). Also, recent studies have used the width of this emission line as a proxy for the stellar velocity dispersion in the host galaxy. This paper calls both of these assumptions into question by analyzing a sample of approximately 400 AGN spectra from the first data release of the Sloan Digital Sky Survey.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A74
- Title:
- Bootes field deep LOFAR 150MHz imaging
- Short Name:
- J/A+A/620/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a deep survey (with a central rms of 55uJy) with the LOw Frequency ARray (LOFAR) at 120-168MHz of the Bootes field, with an angular resolution of 3.98"x6.45", and obtained a sample of 10091 radio sources (5{sigma} limit) over an area of 20deg^2^. The astrometry and flux scale accuracy of our source catalog is investigated. The resolution bias, incompleteness and other systematic effects that could affect our source counts are discussed and accounted for. The derived 150MHz source counts present a flattening below sub-mJy flux densities, that is in agreement with previous results from high- and low- frequency surveys. This flattening has been argued to be due to an increasing contribution of star-forming galaxies and faint active galactic nuclei. Additionally, we use our observations to evaluate the contribution of cosmic variance to the scatter in source counts measurements. The latter is achieved by dividing our Bootes mosaic into 10 non-overlapping circular sectors, each one with an approximate area of 2deg^2^. The counts in each sector are computed in the same way as done for the entire mosaic. By comparing the induced scatter with that of counts obtained from depth observations scaled to 150MHz, we find that the 1{sigma} scatter due to cosmic variance is larger than the Poissonian errors of the source counts, and it may explain the dispersion from previously reported depth source counts at flux densities S<1mJy. This work demonstrates the feasibility of achieving deep radio imaging at low-frequencies with LOFAR.
