Abstract
We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased ...sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median
z
= 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δ
i
= 0.6 mag) and redder (Δ(
g
−
i
) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)–65% of these, at
z
< 0.5 are galaxies without strong nuclear emission, and 10% at
z
> 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (
z
em
= 3.132), and the largest radio source (size ∼330 kpc) is M0909-3133 (
z
em
= 0.884). We discuss in detail 110 AGN at 1.9 <
z
< 3.5. Despite representing the radio loudest quasars (median
R
= 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower
R
. We detect four C
iv
broad-absorption line (BAL) QSOs, all among AGN with least
R
, and highest black hole masses and Eddington ratios. The BAL detection rate (
4
−
2
+
3
%) is consistent with that seen in extremely powerful (
L
1.4GHz
> 10
25
W Hz
−1
) quasars. Using optical light curves, radio polarization, and
γ
-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H
i
21 cm and OH 18 cm lines at
z
< 2.
Abstract
The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at the
L
band (900–1670 MHz) at
δ
≲ +20°. We present radio continuum images and a catalog of 495,325 (240,321) ...radio sources detected at a signal-to-noise ratio (S/N) > 5 over an area of 2289 deg
2
(1132 deg
2
) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source (
S
1 GHz
≳ 0.2 Jy). The median spatial resolution is 12″ (8″). The median rms noise away from the pointing center is 25
μ
Jy beam
−1
(22
μ
Jy beam
−1
) and is within ∼15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are <1% (8% scatter) and 1″, respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog’s accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and 0.″8, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices (
α
) of a subset of 125,621 sources (S/N > 8), confirm the flattening of spectral indices with decreasing flux density, and identify 140 ultra-steep-spectrum (
α
< −1.3) sources as prospective high-
z
radio galaxies (
z
> 2). We have identified 1308 variable and 122 transient radio sources comprising primarily active galactic nuclei that demonstrate long-term (26 yr) variability in their observed flux densities. The MALS catalogs and images are publicly available at
https://mals.iucaa.in
.
ABSTRACT We analyze the relationships between atomic, neutral hydrogen (H i) and star formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral (∼0.82 km s−1 ch−1) and spatial ...resolution (physical resolutions of 160-640 pc) H i imaging from the VLA with Hα and far-ultraviolet imaging. We quantify the degree of co-spatiality between star-forming regions and regions of high H i column densities. We calculate the global star formation efficiencies (SFE; / ) and examine the relationships among the SFE and H i mass, H i column density, and star formation rate (SFR). The systems are consuming their cold neutral gas on timescales of order a few gigayears. While we derive an index for the Kennicutt-Schmidt relation of N ≈ 0.68 ± 0.04 for the SHIELD sample as a whole, the values of N vary considerably from system to system. By supplementing SHIELD results with those from other surveys, we find that H i mass and UV-based SFR are strongly correlated over five orders of magnitude. Identification of patterns within the SHIELD sample allows us to bin the galaxies into three general categories: (1) mainly co-spatial H i and SF regions, found in systems with the highest peak H i column densities and highest total H i masses; (2) moderately correlated H i and SF regions, found in systems with moderate H i column densities; and (3) obvious offsets between H i and SF peaks, found in systems with the lowest total H i masses. SF in these galaxies is dominated by stochasticity and random fluctuations in their ISM.
One of the key goals of the Bluedisk survey is to characterize the impact of gas accretion in disc galaxies in the context of galaxy evolution. It contains 50 disc galaxies in the stellar mass range ...10 super( 10)-10 super( 11) M..., of which half are bluer and more H i-rich galaxies than their H i-normal (control) counterparts. In this paper, we investigate how ongoing disc growth affects the molecular gas distribution and the star formation efficiency in these galaxies. We present super( 12)CO observations from the IRAM 30-m telescope in 26 galaxies of the Bluedisk survey. We compare the amount and spatial distribution of the molecular gas to key quantities such as atomic gas, stellar mass and surface density, star formation rate (SFR) and metallicity. We analyse the SFR per unit gas (SFR/H i and SFR/H sub( 2)) and relate all those parameters to general galaxy properties (H i-rich/control disc, morphology, etc.). We find that the H i-rich galaxies have similar H sub( 2) masses as the control galaxies. In their centres, H i-rich galaxies have lower H sub( 2)/H i ratios and marginally shorter molecular gas depletion times. However, the main differences between the two samples occur in the outer parts of the discs, with the H i-rich galaxies having slightly smaller CO discs (relative to the optical radius R sub( 25)) and steeper CO and metallicity gradients than the control galaxies. The ongoing accretion of H i at large radii has thus not led to an appreciable growth of the CO discs in our sample. Based on depletion times, we estimate that this gas will contribute to star formation on time-scales of at least 5 Gyr. (ProQuest: ... denotes formulae/symbols omitted.)
HALOGAS: Extraplanar gas in NGC 3198 Gentile, G.; Józsa, G. I. G.; Serra, P. ...
Astronomy and astrophysics (Berlin),
06/2013, Letnik:
554
Journal Article
Recenzirano
Odprti dostop
We present the analysis of new, deep Hi observations of the spiral galaxy NGC 3198 as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey, with the main aim of investigating ...the presence, amount, morphology, and kinematics of extraplanar gas. We present models of the Hi observations of NGC 3198. The model that matches best the observed data cube features a thick disk with a scale height of ~3 kpc and an Hi mass of about 15% of the total Hi mass; this thick disk also has a decrease in rotation velocity as a function of height (lag) of 7–15 km s-1 kpc-1 (though with large uncertainties). This extraplanar gas is detected for the first time in NGC 3198. Radially, this gas appears to extend slightly beyond the actively star-forming body of the galaxy (as traced by the Hα emission), but it is not more radially extended than the outer, fainter parts of the stellar disk. Compared to previous studies, thanks to the improved sensitivity we trace the rotation curve out to larger radii. We model the rotation curve in the framework of modified Newtonian dynamics (MOND) and confirm that, with the allowed distance range we assumed, fit quality is modest in this galaxy, but the new outer parts are explained in a satisfactory way.
Abstract
We report on the detection of a large, extended H
i
cloud complex in the Galaxy and Mass Survey G23 field, located at a redshift of
z
∼ 0.03, observed as part of the MeerKAT Habitat of ...Galaxies Survey campaign (a pilot survey to explore the mosaicing capabilities of the MeerKAT telescope). The cloud complex, with a total mass of 10
10.0
M
⊙
, lies in proximity to a large galaxy group with
M
dyn
∼ 10
13.5
M
⊙
. We identify seven H ɪ peak concentrations, interconnected as a tenuous
chain
structure, extending ∼400 kpc from east to west, with the largest (central) concentration containing 10
9.7
M
⊙
in H ɪ gas distributed across 50 kpc. The main source is not detected in ultraviolet, optical, or infrared imaging. The implied gas mass-to-light ratio (
M
H I
/
L
r
) is extreme (>1000) even in comparison to other
dark clouds
. The complex has very little kinematic structure (110 km s
−1
), making it difficult to identify cloud rotation. Assuming pressure support, the total mass of the central concentration is > 10
10.2
M
⊙
, while a lower limit to the dynamical mass in the case of full rotational support is 10
10.4
M
⊙
. If the central concentration is a stable structure, it has to contain some amount of unseen matter, but potentially less than is observed for a typical galaxy. It is, however, not clear whether the structure has any gravitationally stable concentrations. We report a faint UV-optical-infrared source in proximity to one of the smaller concentrations in the gas complex, leading to a possible stellar association. The system nature and origins is enigmatic, potentially being the result of an interaction with or within the galaxy group it appears to be associated with.
H I content in Coma cluster substructure Healy, J.; Blyth, S.-L.; Verheijen, M. A. W. ...
Astronomy and astrophysics (Berlin),
06/2021, Letnik:
650
Journal Article
Recenzirano
Odprti dostop
Context.
Galaxy clusters are some of largest structures in the universe. These very dense environments tend to be home to higher numbers of evolved galaxies than found in lower-density environments. ...It is well known that dense environments can influence the evolution of galaxies through the removal of the neutral gas (H
I
) reservoirs that fuel star formation. It is unclear which environment has a stronger effect: the local environment (i.e., the substructure within the cluster), or the cluster itself.
Aims.
Using the new H
I
data from the Westerbork Coma Survey, we explore the average H
I
content of galaxies across the cluster comparing galaxies that reside in substructure to those that do not.
Methods.
We applied the Dressler–Shectman test to our newly compiled redshift catalogue of the Coma cluster to search for substructure. With so few of the Coma galaxies directly detected in H
I
, we used the H
I
stacking technique to probe the average H
I
content below what can be directly detected.
Results.
Using the Dressler–Shectman test, we find 15 substructures within the footprint of the Westerbork Coma Survey. We compare the average H
I
content for galaxies within substructure to those not in substructure. Using the H
I
stacking technique, we find that those Coma galaxies not detected in H
I
are more than 10–50 times more H
I
deficient than expected, which supports the scenario of an extremely efficient and rapid quenching mechanism. By studying the galaxies that are not directly detected in H
I
, we also find Coma to be more H
I
deficient than previously thought.
We introduce the 'Bluedisk' project, a large programme at the Westerbork Synthesis Radio Telescope that has mapped the H i in a sample of 23 nearby galaxies with unusually high H i mass fractions, ...along with a similar-sized sample of control galaxies. This paper presents the sample selection, observational set-up, data reduction strategy and a first analysis of the sizes and structural properties of the H i discs. We find that the H i-rich galaxies lie on the same H i mass versus H i size relation as normal spiral galaxies, extending it to total H i masses of 2 × 1010 M and radii R1 of ∼100 kpc. The H i-rich galaxies have significantly larger values of H i-to-optical size ratio and more clumpy H i
discs than those of normal spirals. There is no evidence that the discs of H i-rich galaxies are more disturbed. In fact, the centre of the H i
distribution corresponds more closely with the centre of the optical light in the H i-rich galaxies than in the controls. All these results argue against a scenario in which new gas has been brought in by mergers. It is possible that they may be more consistent with cooling from a surrounding quasi-static halo of warm/hot gas.
Abstract
The identification of active galactic nuclei (AGNs) in large surveys has been hampered by seemingly discordant classifications arising from differing diagnostic methods, usually tracing ...distinct processes specific to a particular wavelength regime. However, as shown in Yao et al., the combination of optical emission-line measurements and mid-infrared photometry can be used to optimize the discrimination capability between AGN and star formation activity. In this paper we test our new classification scheme by combining the existing GAMA-WISE data with high-quality MeerKAT radio continuum data covering 8 deg
2
of the GAMA G23 region. Using this sample of 1841 galaxies (
z
< 0.25), we investigate the total infrared (derived from 12
μ
m) to radio luminosity ratio,
q
(TIR)
, and its relationship to optical–infrared AGN and star-forming (SF) classifications. We find that while
q
(TIR)
is efficient at detecting AGN activity in massive galaxies generally appearing quiescent in the infrared, it becomes less reliable for cases where the emission from star formation in the host galaxy is dominant. However, we find that the
q
(TIR)
can identify up to 70% more AGNs not discernible at optical and/or infrared wavelengths. The median
q
(TIR)
of our SF sample is 2.57 ± 0.23, consistent with previous local universe estimates.
ABSTRACT
The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H i) is an excellent way to trace these interactions. Here, we ...present H i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH$\_$J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09M⊙/yr, a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H i and optical to reveal a more complete picture of galaxy environments.
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