- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/2385
- Title:
- Bootes field LOFAR 150-MHz observations
- Short Name:
- J/MNRAS/460/2385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first wide area (19 deg^2^), deep (~=120-150 {mu}Jy/beam), high-resolution (5.6x7.4-arcsec) LOFAR High Band Antenna image of the Bootes field made at 130-169MHz. This image is at least an order of magnitude deeper and 3-5 times higher in angular resolution than previously achieved for this field at low frequencies. The observations and data reduction, which includes full direction-dependent calibration, are described here. We present a radio source catalogue containing 6276 sources detected over an area of 19deg^2^, with a peak flux density threshold of 5{sigma}. As the first thorough test of the facet calibration strategy, introduced by van Weeren et al. (2016ApJS..223....2V), we investigate the flux and positional accuracy of the catalogue. We present differential source counts that reach an order of magnitude deeper in flux density than previously achieved at these low frequencies, and show flattening at 150-MHz flux densities below 10 mJy associated with the rise of the low flux density star-forming galaxies and radio-quiet AGN.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/629
- Title:
- Bootes-HiZELS. Em-line galaxies at z=0.4-4.7
- Short Name:
- J/MNRAS/471/629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of ~1000 emission-line galaxies at z=0.4-4.7 from the ~0.7deg^2^ High-z Emission-Line Survey in the Bootes field identified with a suite of six narrow-band filters at ~=0.4-2.1{mu}m. These galaxies have been selected on their Ly{alpha} (73), [OII] (285), H{beta}/[OIII] (387) or H{alpha} (362) emission line, and have been classified with optical to near-infrared colours. A subsample of 98 sources have reliable redshifts from multiple narrow-band (e.g. [OII]-H{alpha}) detections and/or spectroscopy. In this survey paper, we present the observations, selection and catalogues of emitters. We measure number densities of Ly{alpha}, [OII], H{beta}/[OIII] and H{alpha} and confirm strong luminosity evolution in star-forming galaxies from z~0.4 to ~5, in agreement with previous results. To demonstrate the usefulness of dual-line emitters, we use the sample of dual [OII]-H{alpha} emitters to measure the observed [OII]/H{alpha} ratio at z=1.47. The observed [OII]/H{alpha} ratio increases significantly from 0.40+/-0.01 at z=0.1 to 0.52+/-0.05 at z=1.47, which we attribute to either decreasing dust attenuation with redshift, or due to a bias in the (typically) fibre measurements in the local Universe that only measure the central kpc regions. At the bright end, we find that both the H{alpha} and Ly{alpha} number densities at z~=2.2 deviate significantly from a Schechter form, following a power law. We show that this is driven entirely by an increasing X-ray/active galactic nucleus fraction with line luminosity, which reaches ~=100 per cent at line luminosities L>=3x10^44^erg/s.
- ID:
- ivo://CDS.VizieR/J/MNRAS/418/1055
- Title:
- BOSS morphology of galaxies
- Short Name:
- J/MNRAS/418/1055
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the morphology and size of the luminous and massive galaxies at 0.3<z<0.7 targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly available Hubble Space Telescope (HST) imaging, and catalogues, from the COSMic Origins Survey (COSMOS). Our sample (240 objects) provides a unique opportunity to check the visual morphology of these galaxies which were targeted based solely on stellar population modelling.
- ID:
- ivo://CDS.VizieR/J/A+AS/145/405
- Title:
- Box- and peanut-shaped bulges. I.
- Short Name:
- J/A+AS/145/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NIR observations reveal that dust extinction does almost not influence the shape of bulges. There is no substantial difference between the shape of bulges in the optical and in the NIR. Our analysis reveals that 45% of all bulges are box- and peanut-shaped (b/p). The frequency of b/p bulges for all morphological types from S0 to Sd is >40%. In particular, this is for the first time that such a large frequency of b/p bulges is reported for galaxies as late as Sd. The fraction of the observed b/p bulges is large enough to explain the origin of b/p bulges by a barred potential (Luetticke et al., 2000, A&A, accepted).
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/2058
- Title:
- Boxy/peanut-shaped bulges in barred galaxies
- Short Name:
- J/MNRAS/468/2058
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From a sample of 84 local barred, moderately inclined disc galaxies, we determine the fraction that hosts boxy or peanut-shaped (B/P) bulges (the vertically thickened inner parts of bars). We find that the frequency of B/P bulges in barred galaxies is a very strong function of stellar mass: 79 per cent of the bars in galaxies with log (M*/M_{sun}_)w>=10.4 have B/P bulges, while only 12 per cent of those in lower mass galaxies do. (We find a similar dependence in data published by Yoshino & Yamauchi for edge-on galaxies.) There are also strong trends with other galaxy parameters - e.g. Hubble type: 77 per cent of S0-Sbc bars, but only 15 per cent of Sc-Sd bars, have B/P bulges - but these appear to be side effects of the correlations of these parameters with stellar mass. In particular, despite indications from models that a high gas content can suppress bar buckling, we find no evidence that the (atomic) gas mass ratio M_HI+He_/M* affects the presence of B/P bulges, once the stellar-mass dependence is controlled for. The semimajor axes of B/P bulges range from one-quarter to three-quarters of the full bar size, with a mean of R_box_/L_bar_=0.42+/-0.09 and R_box_/a_{epsilon}_=0.53+/-0.12 (where R_box_ is the size of the B/P bulge and a_{epsilon}_ and L_bar_ are lower and upper limits on the size of the bar).
- ID:
- ivo://CDS.VizieR/J/A+A/622/A209
- Title:
- B2 0258+35 polarisation images
- Short Name:
- J/A+A/622/A209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The contribution of active galactic nuclei to the magnetisation of the Universe can be constrained by knowing their duty cycles, jet and magnetic field morphologies, and the physical processes dominating their interaction with the surrounding environment. The magnetic field morphology and strength of radio lobes of AGN has an influence on the mechanisms for the propagation of cosmic rays into intergalactic space. Using the source B2 0258+35 we want to investigate the interaction of its radio lobes with the surrounding environment and examine the underlying physical effects. Published HI and radio continuum data at {lambda}21cm were combined with newly reduced archival Westerbork Radio Synthesis Telescope polarisation data at the same wavelength to investigate the polarised emission in the radio lobes of B2 0258+35. We assumed energy equipartition between the cosmic rays and the magnetic field to calculate their pressure and investigate the physical processes leading to the detected emission. We detected a unique S-shaped diffuse polarised structure. The lobes have a pressure of p=1.95+/-0.4x10^-14^dyn/cm^2^. The calculated total magnetic field strengths are low (B_eq_=1.21+/-0.12uG). We observe depolarisation in the northern lobe, which might originate from the HI-disc in the foreground. In addition we see an anti-correlation between the pressure and the fractional polarisation along the S-shaped structure. Therefore we consider magnetic draping and magnetic field compression as possible effects that might have created the observed S-shape. Our results suggest that magnetic draping can be effectively used to explain the observed polarised structures. This is likely due to the combination of a relatively low magnetic field strength, enabling super-Alfvenic motion of the rising lobes (with M_A_=2.47-3.50), and the coherency of the surrounding magnetic field. Moreover, the draped layer tends to suppress any mixing of the material between the radio lobes and the surrounding environment, but can enhance the mixing and re-acceleration efficiencies inside the lobes, providing an explanation for the average flat spectral index observed in the lobes.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A127
- Title:
- Breaks in disc galaxy abundance gradients
- Short Name:
- J/A+A/608/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the relation between breaks in the surface brightness profiles and radial abundance gradients within the optical radius in the discs of 134 spiral galaxies from the CALIFA survey. The distribution of the radial abundance (in logarithmic scale) in each galaxy was fitted by simple and broken linear relations. The surface brightness profile was fitted assuming pure and broken exponents for the disc. We find that the maximum absolute difference between the abundances in a disc given by broken and pure linear relations is less than 0.05dex in the majority of our galaxies and exceeds the scatter in abundances for 26 out of 134 galaxies considered. The scatter in abundances around the broken linear relation is close (within a few percent) to that around the pure linear relation. The breaks in the surface brightness profiles are more prominent. The scatter around the broken exponent in a number of galaxies is lower by a factor of two or more than that around the pure exponent. The shapes of the abundance gradients and surface brightness profiles within the optical radius in a galaxy may be different. A pure exponential surface brightness profile may be accompanied by a broken abundance gradient and vise versa. There is no correlation between the break radii of the abundance gradients and surface brightness profiles. Thus, a break in the surface brightness profile does not need to be accompanied by a break in the abundance gradient.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A36
- Title:
- Breaks in surf. brightness prof. of galaxy disks
- Short Name:
- J/A+A/625/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a sample of 175 low-inclination galaxies from the S^4^G, we investigate the origins of up-bending (Type III) breaks in the 3.6{mu}m surface brightness profiles of disk galaxies. We reanalyzed a sample of previously identified Type III disk break-hosting galaxies using a new, unbiased break-finding algorithm, which uncovered many new, sometimes subtle disk breaks across the whole sample. We classified each break by its likely origin through close examination of the galaxy images across wavelengths, and compare samples of galaxies separated by their outermost identified break types in terms of their stellar populations and local environments. We find that more than half of the confirmed Type III breaks in our sample can be attributed to morphological asymmetry in the host galaxies. As these breaks are mostly an artifact of the azimuthal averaging process, their status as physical breaks is questionable. Such galaxies occupy some of the highest density environments in our sample, implying that much of this asymmetry is the result of tidal disturbance. We also find that Type III breaks related to extended spiral arms or star formation often host down-bending (Type II) breaks at larger radius which were previously unidentified. Such galaxies reside in the lowest density environments in our sample, in line with previous studies that found a lack of Type II breaks in clusters. Galaxies occupying the highest density environments most often show Type III breaks associated with outer spheroidal components. We find that Type III breaks in the outer disks of galaxies arise most often through environmental influence: either tidal disturbance (resulting in disk asymmetry) or heating through, for example, galaxy harrassment (leading to spheroidal components). Galaxies hosting the latter break types also show bimodal distributions in central g-r color and morphological type, with more than half of such galaxies classified as Sa or earlier; this suggests these galaxies may be evolving into early-type galaxies. By contrast, we find that Type III breaks related to apparently secular features (e.g., spiral arms) may not truly define their hosts' outer disks, as often in such galaxies additional significant breaks can be found at larger radius. Given this variety in Type III break origins, we recommend in future break studies making a more detailed distinction between break subtypes when seeking out, for example, correlations between disk breaks and environment, to avoid mixing unlike physical phenomena.
- ID:
- ivo://CDS.VizieR/J/ApJS/147/29
- Title:
- BRHalpha data of blue compact dwarf galaxies
- Short Name:
- J/ApJS/147/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present B, R, and H{alpha} images for a total of 114 nearby galaxies (v_helio_<4000km/s) that, with exception of nine objects, are classified as blue compact dwarfs (BCDs). BR integrated magnitudes, H{alpha} fluxes and H{alpha} equivalent widths for all the objects in the sample are presented.