This paper describes the on-telescope performance of the Wide Field Spectrograph (WiFeS). The design characteristics of this instrument, at the Research School of Astronomy and Astrophysics (RSAA) of ...the Australian National University (ANU) and mounted on the ANU 2.3 m telescope at the Siding Spring Observatory has been already described in an earlier paper (Dopita et al. in Astrophys. Space Sci. 310:255,
2007
). Here we describe the throughput, resolution and stability of the instrument, and describe some minor issues which have been encountered. We also give a description of the data reduction pipeline, and show some preliminary results.
Abstract
We measure how the atomic gas (H
i
) fraction
f
H
I
=
M
H
I
M
*
of groups and pairs taken as single units vary with average stellar mass (〈
M
*
〉) and average star formation rate (〈SFR〉), ...compared to isolated galaxies. The H
i
21 cm emission observation are from (i) archival ALFALFA survey data covering three fields from the GAMA survey (provides environmental and galaxy properties), and (ii) DINGO pilot survey data of one of those fields. The mean
f
H
i
for different units (groups/pairs/isolated galaxies) are measured in regions of the log(〈
M
*
〉)–log(〈SFR〉) plane, relative to the
z
∼ 0 star-forming main sequence (SFMS) of individual galaxies, by stacking
f
H
i
spectra of individual units. For ALFALFA,
f
H
i
spectra of units are measured by extracting H
i
spectra over the full groups/pair areas and dividing by the total stellar mass of member galaxies. For DINGO,
f
H
i
spectra of units are measured by co-adding H
i
spectra of individual member galaxies, followed by division by their total stellar mass. For all units, the mean
f
H
i
decreases as we move to higher 〈
M
*
〉 along the SFMS and as we move from above the SFMS to below it at any 〈
M
*
〉. From the DINGO-based study, mean
f
H
i
in groups appears to be lower compared to isolated galaxies for all 〈
M
*
〉 along the SFMS. From the ALFALFA-based study, we find substantially higher mean
f
H
i
in groups compared to isolated galaxies (values for pairs being intermediate) for 〈
M
*
〉 ≲ 10
9.5
M
⊙
, indicating the presence of substantial amounts of H
i
not associated with cataloged member galaxies in low mass groups.
Abstract
Combining new H
i
data from a synergetic survey of Australian Square Kilometre Array Pathfinder (ASKAP) Widefield ASKAP
L
-band Legacy All-sky Blind surveY and Five-hundred-meter Aperture ...Spherical radio Telescope with the Arecibo Legacy Fast ALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in H
i
-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of H
i
-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of H
i
-detected nonmerging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two H
i
-stripping extents moderately anticorrelate with each other. Both strengths are correlated with H
i
-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies (
M
*
< 10
9
M
☉
) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of H
i
richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from ∼1 Gyr beyond
R
200
to ≲10 Myr near the center. Gas depletion happens ∼3 Gyr since crossing 2
R
200
for H
i
-rich galaxies, but much quicker for H
i
-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way.
Abstract
We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (H i) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at z ...≈ 0.32. Because the H i emission from individual galaxies is too faint to detect at this redshift, we use an H i spectral stacking technique using the known optical positions and redshifts of the 165 galaxies in our sample to co-add their H i spectra and thus obtain the average H i mass of the galaxies. Stacked H i measurements of 165 galaxies show that ≳ 95 per cent of the neutral gas is found in blue, star-forming galaxies. Among these galaxies, those having lower stellar mass are more gas rich than more massive ones. We apply a volume correction to our H i measurement to evaluate the H i gas density at z ≈ 0.32 as ${\Omega _{\rm {H}\, \small {I}}}=(0.50\pm 0.18)\times\, 10^{-3}$ in units of the cosmic critical density. This value is in good agreement with previous results at z < 0.4, suggesting no evolution in the neutral hydrogen gas density over the last ∼4 Gyr. However the z ≈ 0.32 gas density is lower than that at z ∼ 5 by at least a factor of two.
ABSTRACT
Measuring the H i–halo mass scaling relation (HIHM) is fundamental to understanding the role of H i in galaxy formation and its connection to structure formation. While direct measurements ...of the H i mass in haloes are possible using H i-spectral stacking, the reported shape of the relation depends on the techniques used to measure it (e.g. monotonically increasing with mass versus flat, mass-independent). Using a simulated H i and optical survey produced with the shark semi-analytic galaxy formation model, we investigate how well different observational techniques can recover the intrinsic, theoretically predicted, HIHM relation. We run a galaxy group finder and mimic the H i stacking procedure adopted by different surveys and find we can reproduce their observationally derived HIHM relation. However, none of the adopted techniques recover the underlying HIHM relation predicted by the simulation. We find that systematic effects in halo mass estimates of galaxy groups modify the inferred shape of the HIHM relation from the intrinsic one in the simulation, while contamination by interloping galaxies, not associated with the groups, contribute to the inferred H i mass of a halo mass bin, when using large velocity windows for stacking. The effect of contamination is maximal at $M^{\rm }_{\rm vir}$$\sim 10^{12-12.5}\rm M_{\odot }$. Stacking methods based on summing the H i emission spectra to infer the mean H i mass of galaxies of different properties belonging to a group suffer minimal contamination but are strongly limited by the use of optical counterparts, which miss the contribution of dwarf galaxies. Deep spectroscopic surveys will provide significant improvements by going deeper while maintaining high spectroscopic completeness; for example, the WAVES survey will recover ∼52 per cent of the total H i mass of the groups with $M^{\rm }_{\rm vir}$ ∼ 1014M⊙ compared to ∼21 per cent in GAMA.
ABSTRACT
We determine the atomic hydrogen (H i) to halo mass relation (HIHM) using Arecibo Legacy Fast ALFA survey H i data at the location of optically selected groups from the Galaxy And Mass ...Assembly (GAMA) survey. We make direct H i detections for 37 GAMA groups. Using H i group spectral stacking of 345 groups, we study the group H i content as a function of halo mass across a halo mass range of 1011–1014.7 M⊙. We also correct our results for Eddington bias. We find that the group H i mass generally rises as a function of halo mass from 1.3% of the halo mass at $10^{11.6} \, \text{M}_\odot$ to 0.4% at $10^{13.7} \, \text{M}_\odot$ with some indication of flattening towards the high-mass end. Despite the differences in optical survey limits, group catalogues, and halo mass estimation methods, our results are consistent with previous group H i-stacking studies. Our results are also consistent with mock observations from shark and IllustrisTNG.
ABSTRACT
We present early science results from Deep Investigation of Neutral Gas Origins (DINGO), an $\rm H$i survey using the Australian Square Kilometre Array Pathfinder (ASKAP). Using ASKAP ...subarrays available during its commissioning phase, DINGO early science data were taken over ∼60 deg2 of the Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 h integration time. We make direct detections of six known and one new sources at z < 0.01. Using $\rm H$ i spectral stacking, we investigate the $\rm H$ i gas content of galaxies at 0.04 < z < 0.09 for different galaxy colours. The results show that galaxy morphology based on optical colour is strongly linked to $\rm H$ i gas properties. To examine environmental impacts on the $\rm H$i gas content of galaxies, three subsamples are made based on the GAMA group catalogue. The average $\rm H$i mass of group central galaxies is larger than those of satellite and isolated galaxies, but with a lower $\rm H$i gas fraction. We derive a variety of $\rm H$i scaling relations for physical properties of our sample, including stellar mass, stellar mass surface density, NUV − r colour, specific star formation rate, and halo mass. We find that the derived $\rm H$i scaling relations are comparable to other published results, with consistent trends also observed to ∼0.5 dex lower limits in stellar mass and stellar surface density. The cosmic $\rm H$i densities derived from our data are consistent with other published values at similar redshifts. DINGO early science highlights the power of $\rm H$i spectral stacking techniques with ASKAP.
ABSTRACT
Galaxy morphology in atomic hydrogen (H i) and in the ultraviolet (UV) are closely linked. This has motivated their combined use to quantify morphology over the full H i disc for both H i ...and UV imaging. We apply galaxy morphometrics: concentration, asymmetry, gini, M20 and multimode-intensity-deviation statistics to the first moment-0 maps of the WALLABY Survey of galaxies in the hydra cluster centre. Taking advantage of this new H i survey, we apply the same morphometrics over the full H i extent on archival GALEX FUV and NUV data to explore how well H i truncated, extended ultraviolet disc (XUV) and other morphological phenomena can be captured using pipeline WALLABY data products. Extended H i and UV discs can be identified relatively straightforward from their respective concentration. Combined with WALLABY H i, even the shallowest GALEX data are sufficient to identify XUV discs. Our second goal is to isolate galaxies undergoing ram-pressure stripping in the H i morphometric space. We employ four different machine learning techniques, a decision tree, a k-nearest neighbour, a support-vector machine, and a random forest. Up to 80 per cent precision and recall are possible with the random forest giving the most robust results.
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