Abstract
We study the environments of low- and high-excitation radio galaxies (LERGs and HERGs, respectively) in the redshift range 0.01 < z < 0.4, using a sample of 399 radio galaxies and ...environmental measurements from the Galaxy And Mass Assembly (GAMA) survey. In our analysis we use the fifth nearest neighbour density (Σ5) and the GAMA galaxy groups catalogue (G3Cv6) and construct control samples of galaxies matched in stellar mass and colour to the radio-detected sample. We find that LERGs and HERGs exist in different environments and that this difference is dependent on radio luminosity. High-luminosity LERGs (L
NVSS ≳ 1024 W Hz−1) lie in much denser environments than a matched radio-quiet control sample (about three times as dense, as measured by Σ5), and are more likely to be members of galaxy groups (
$82^{+5}_{-7}$
per cent of LERGs are in GAMA groups, compared to
$58^{+3}_{-3}$
per cent of the control sample.). In contrast, the environments of the HERGs and lower luminosity LERGs are indistinguishable from that of a matched control sample. Our results imply that high-luminosity LERGs lie in more massive haloes than non-radio galaxies of similar stellar mass and colour, in agreement with earlier studies. When we control for the preference of LERGs to be found in groups, both high- and low-luminosity LERGs are found in higher-mass haloes (∼0.2 dex; at least 97 per cent significant) than the non-radio control sample.
We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially resolved signatures of the ...environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of H... emission, we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M*; 10 super( 8.1)-10 super( 10.95) M...) and in fifth nearest neighbour local environment density (...; 10 super( -1.3)-10 super( 2.1) Mpc super( -2)). We show that star formation rate gradients in galaxies are steeper in dense (log sub( 10)(.../Mpc super( 2)) > 0.5) environments by 0.58 plus or minus 0.29dexr sub( e) super( -1) in galaxies with stellar masses in the range 10 super( 10)<M*/M...<10 super( 11) and that this steepening is accompanied by a reduction in the integrated star formation rate. However, for any given stellar mass or environment density, the star formation morphology of galaxies shows large scatter. We also measure the degree to which the star formation is centrally concentrated using the unitless scale-radius ratio (r sub( 50,H...)/r sub( 50,cont)), which compares the extent of ongoing star formation to previous star formation. With this metric, we find that the fraction of galaxies with centrally concentrated star formation increases with environment density, from ~5 plus or minus 4 per cent in low-density environments (log sub( 10)(.../Mpc super( 2)) < 0.0) to 30 plus or minus 15 per cent in the highest density environments (log sub( 10)(.../Mpc super( 2)) > 1.0). These lines of evidence strongly suggest that with increasing local environment density, the star formation in galaxies is suppressed, and that this starts in their outskirts such that quenching occurs in an outside-in fashion in dense environments and is not instantaneous. (ProQuest: ... denotes formulae/symbols omitted.)
The H i content of star-forming galaxies at z= 0.24 Lah, Philip; Chengalur, Jayaram N.; Briggs, Frank H. ...
Monthly notices of the Royal Astronomical Society,
04/2007, Volume:
376, Issue:
3
Journal Article
Peer reviewed
Open access
We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star-forming galaxies at z= 0.24 (i.e. a look-back time of ∼3 Gyr). The sample of ...galaxies studied were selected from Hα-emitting field galaxies detected in a narrow-band imaging survey with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain precise optical redshifts for these galaxies. We then co-added the H i 21-cm emission signal for all the galaxies within the GMRT spectral line data cube. From the co-added signal of 121 galaxies, we measure an average atomic hydrogen gas mass of (2.26 ± 0.90) × 109 M⊙. We translate this H i signal into a cosmic density of neutral gas at z= 0.24 of Ωgas= (0.91 ± 0.42) × 10−3. This is the current highest redshift at which Ωgas has been constrained from 21-cm emission and our value is consistent with that estimated from damped Lyα systems around this redshift. We also find that the correlations between the Hα luminosity and the radio continuum luminosity and between the star formation rate (SFR) and the H i gas content in star-forming galaxies at z= 0.24 are consistent with the correlations found at z= 0. These two results suggest that the star formation mechanisms in field galaxies ∼3 Gyr ago were not substantially different from the present, even though the SFR is three times higher.
We present the results of a targeted search for intervening H i absorption in six nearby, gas-rich galaxies using the Australia Telescope Compact Array. The sightlines searched have impact parameters ...of 10–20 kpc. By targeting nearby galaxies, we are also able to map their H i emission, allowing us to directly relate the absorption-line detection rate to the extended H i distribution. The continuum sightlines intersect the H i disc in four of the six galaxies, but no intervening absorption was detected. Of these four galaxies, we find that three of the non-detections are the result of the background source being too faint. In the fourth case, we find that the ratio of the spin temperature to the covering factor (T
S/f) must be much higher than expected (≳5700 K) in order to explain the non-detection. We discuss how the structure of the background continuum sources may have affected the detection rate of H i absorption in our sample, and the possible implications for future surveys. Future work including an expanded sample, and very long baseline interferometry observations, would allow us to better investigate the expected detection rate, and influence of background source structure, on the results of future surveys.
We present the results of a survey for intervening 21 cm H i absorption in a sample of 10 nearby, gas-rich galaxies selected from the H i Parkes All-Sky Survey (HIPASS). This follows the six HIPASS ...galaxies searched in previous work and completes our full sample. In this paper, we searched for absorption along 17 sightlines with impact parameters between 6 and 46 kpc, making one new detection. We also obtained simultaneous H i emission-line data, allowing us to directly relate the absorption-line detection rate to the H i distribution. From this, we find the majority of the non-detections in the current sample are because sightline does not intersect the H i disc of the galaxy at sufficiently high column density, but that source structure is also an important factor. The detected absorption-line arises in the galaxy NGC 5156 (z = 0.01) at an impact parameter of 19 kpc. The line is deep and narrow with an integrated optical depth of 0.82 km s−1. High-resolution Australia Telescope Compact Array (ATCA) images at 5 and 8 GHz reveal that the background source is resolved into two components with a separation of 2.6 arcsec (500 pc at the redshift of the galaxy), with the absorption likely occurring against a single component. We estimate that the ratio of the spin temperature and covering factor, T
S/f, is approximately 950 K in the outer disc of NGC 5156, but further observations using very long baseline interferometry would allow us to accurately measure the covering factor and spin temperature of the gas.
We present the results of a survey for H i 21 cm and OH 18 cm absorption in seven strong CO emitters at z ≳ 3. Despite reaching limits comparable to those required to detect 21 cm absorption at lower ...redshifts, we do not detect either transition in any of the objects searched. We believe that this is due to the high-redshift selection causing all of our targets to have ultraviolet (UV) luminosities above the critical value, where all of the atomic gas in the host galaxy disc is suspected to be ionized. However, not only are all of our targets bright in CO emission, but detection of CO above the critical UV luminosity is generally not uncommon. This suggests that the molecular gas is shielded from the radiation or is physically remote from the source of the continuum emission, as it appears to be from CO observations of high-redshift radio galaxies.
We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have ...been able to put sensitive upper limits on the abundances of both molecules. The 3σ upper limits derived for glycine conformer I are 3.7 × 1014 cm−2 in both Orion-KL and Sgr B2 (LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3σ upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of 7.7 × 1012 cm−2 in both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine (both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 × 1014 cm−2 in Orion-KL and 6.7 × 1014 cm−2 in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier.
We present the initial results of a 3-mm spectral-line survey towards 83 methanol maser-selected massive star-forming regions. Here, we report observations of the J = 5–4 and 6–5 rotational ...transitions of methyl cyanide (CH3CN) and the J = 1–0 transition of HCO+ and H13CO+. CH3CN emission is detected in 58 sources (70 per cent of our sample). We estimate the temperature and column density for 37 of these using the rotational diagram (RD) method. The temperatures we derive range from 28–166 K, and are lower than previously reported temperatures, derived from higher J transitions. We find that CH3CN is brighter and more commonly detected towards ultracompact H ii (UCH ii) regions than towards isolated maser sources. Detection of CH3CN towards isolated maser sources strongly suggests that these objects are internally heated and that CH3CN is excited prior to the UCH ii phase of massive star formation. HCO+ is detected towards 82 sources (99 per cent of our sample), many of which exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are indicative of inward or outward motions, however, we find approximately equal numbers of red- and blue-skewed profiles among all classes. Column densities are derived from an analysis of the HCO+ and H13CO+ line profiles. 80 sources have mid-infrared (mid-IR) counterparts: 68 seen in emission and 12 seen in absorption as ‘dark clouds’. Seven of the 12 dark clouds exhibit asymmetric HCO+ profiles, six of which are skewed to the blue, indicating infalling motions. CH3CN is also common in dark clouds, where it has a 90 per cent detection rate.
Abstract
We describe the selection of galaxies targeted in eight low-redshift clusters (APMCC0917, A168, A4038, EDCC442, A3880, A2399, A119 and A85; 0.029 < z < 0.058) as part of the Sydney-AAO ...Multi-Object Integral field spectrograph Galaxy Survey (SAMI-GS). We have conducted a redshift survey of these clusters using the AAOmega multi-object spectrograph on the 3.9-m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterize the dynamical properties of the clusters. In combination with existing data, the survey resulted in 21 257 reliable redshift measurements and 2899 confirmed cluster member galaxies. Our redshift catalogue has a high spectroscopic completeness (∼94 per cent) for rpetro ≤ 19.4 and cluster-centric distances R < 2R200. We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, R200, virial and caustic masses, as well as cluster structure. The clusters have virial masses 14.25 ≤ log(M200/M⊙) ≤ 15.19. The cluster sample exhibits a range of dynamical states, from relatively relaxed-appearing systems, to clusters with strong indications of merger-related substructure. Aperture- and point spread function matched photometry are derived from Sloan Digital Sky Survey and VLT Survey Telescope/ATLAS imaging and used to estimate stellar masses. These estimates, in combination with the redshifts, are used to define the input target catalogue for the cluster portion of the SAMI-GS. The primary SAMI-GS cluster targets have R <R200, velocities |vpec| < 3.5σ200 and stellar masses $9.5 \le {\rm log({\it M}}^*_{{\rm approx}}/$M⊙)≤12. Finally, we give an update on the SAMI-GS progress for the cluster regions.
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