The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. The authors ...present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z similar to 1.2 in the MASSIV survey. Using the N2 ratio between the NII 6584 and H alpha rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, they measured the metallicity of the sample galaxies. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. They suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. They also identify two interesting correlations in their sample: galaxies with higher gas velocity dispersion have shallower/positive gradients; and metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one.
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Aims.
We present the results of three commissioning H
I
observations obtained with the MeerKAT radio telescope. These observations make up part of the preparation for the forthcoming MHONGOOSE ...nearby galaxy survey, which is a MeerKAT large survey project that will study the accretion of gas in galaxies and the link between gas and star formation.
Methods.
We used the available H
I
data sets, along with ancillary data at other wavelengths, to study the morphology of the MHONGOOSE sample galaxy, ESO 302-G014, which is a nearby gas-rich dwarf galaxy.
Results.
We find that ESO 302-G014 has a lopsided, asymmetric outer disc with a low column density. In addition, we find a tail or filament of H
I
clouds extending away from the galaxy, as well as an isolated H
I
cloud some 20 kpc to the south of the galaxy. We suggest that these features indicate a minor interaction with a low-mass galaxy. Optical imaging shows a possible dwarf galaxy near the tail, but based on the current data, we cannot confirm any association with ESO 302-G014. Nonetheless, an interaction scenario with some kind of low-mass companion is still supported by the presence of a significant amount of molecular gas, which is almost equal to the stellar mass, and a number of prominent stellar clusters, which suggest recently triggered star formation.
Conclusions.
These data show that MeerKAT produces exquisite imaging data. The forthcoming full-depth survey observations of ESO 302-G014 and other sample galaxies will, therefore, offer insights into the fate of neutral gas as it moves from the intergalactic medium onto galaxies.
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Interacting galaxies provide us with an excellent laboratory for studying a number of physical phenomena associated with these processes. In this paper, we present a spectroscopic and kinematic ...analysis of the interacting galaxy NGC 4656 and its companion tidal dwarf galaxy (TDG) candidate, NGC 4656UV. Using Fabry-Perot and GMOS multislit data, we investigated the possible origin of NGC 4656UV. We found that NGC 4656UV has a low metallicity (12 + log(O/H)∼8.2) and it follows the mass-metallicity relation for normal dwarf galaxies. For NGC 4656, we estimated a flat oxygen abundance gradient of β = -0.027 ± 0.029 dex kpc-1, which suggests the presence of gas flows induced by gravitational interactions. By analysing radial velocity profiles and by fitting a kinematic model of the observed velocity field, we confirm the literature result that NGC 4656 consists of one single body instead of two objects. We estimated a dynamical mass of 6.8^{1.8}_{-0.6}× 109 M⊙ and R of 12.1 kpc from the kinematic model of NGC 4656. Although the observed velocity field is dominated by rotation at large scales (Vmax/σ ≳2.8), important non-rotational motions are present at small scales. Based on these new results, and on previously published information, we propose that NGC 4656 and 4656UV are a pair of interacting galaxies. NGC 4656UV is a companion of NGC 4656 and it does not have a tidal origin. The interaction between the two could have triggered the star formation in NGC 4656UV and increased the star formation in the north-east side of NGC 4656.
ABSTRACT
We present new Gemini imaging and spectroscopic data of the system Arp 314, which consists of a triplet of interacting galaxies. This new imagery exhibits tidal tails and stellar bridges ...between the galaxies' members and confirms the past interactions. Using this data set, we have analysed the physical properties of 22 star-forming regions located in the main disc of these galaxies, as well as in the intergalactic medium. All these regions have emission lines typical of young ages and a couple of them display very high Hα luminosities (LHα ∼ 1040 erg s−1). Using the star-forming regions located in Arp 314-1, we derive its gas-phase oxygen-abundance distribution, which suggests a flatter behaviour than the distribution shown by non-interacting systems. This is in agreement with results obtained for other interacting systems and simulations. The presence of gas flows, as indicated by its complex kinematics, could explain this finding. Most of the star formation in Arp 314-2 is located in a central starburst, where double Hα profiles can be identified, as shown by archival Fabry–Perot data. Additionally, we found that the irregular galaxy Arp 314-3 has a low oxygen abundance. Considering its luminosity, this object has a primordial origin, and it was not formed during the interaction event that this system has experienced.
Abstract
The aim of this paper is to present the first data set obtained with SOAR Adaptive Module-Fabry–Parot (SAM-FP), a Fabry–Perot instrument mounted inside the SOAR telescope Adaptive-Optics ...Module. This is the only existing imaging Fabry–Perot interferometer using laser-assisted ground-layer adaptive optics. SAM-FP was used to observe the ionized gas, traced by Hα, in the centre of the 30 Doradus starburst (the Tarantula Nebula) in the Large Magellanic Cloud, with high spatial (∼0.6 arcsec, or 0.15 pc) and spectral (R ≃ 11 200) resolution. Radial velocity, velocity dispersion and monochromatic maps were derived. The region displays a mix of narrow, σ ∼ 20 km s−1 profiles and multiple broader profiles with σ ∼ 70–80 km s−1, indicating the complex nature of the nebula kinematics. A comparison with previously obtained VLT/FLAMES spectroscopy demonstrates that the data agree well in the regions of overlap, but the Fabry–Perot data are superior in spatial coverage. A preliminary analysis of the observations finds a new expanding bubble south of R136, with a projected radius of r = 5.6 pc and an expansion velocity of 29 ± 4 km s−1. In addition, the first-time detailed kinematic maps derived here for several complexes and filaments of 30 Doradus allow identification of kinematically independent structures. These data exemplify the power of the combination of a high-order Fabry–Perot with a wide-field imager (3 × 3 arcmin2 GLAO-corrected field of view) for high-resolution spatial and spectral studies. In particular, SAM-FP data cubes are highly advantageous over multifibre or long-slit data sets for nebula structure studies and to search for small-scale bubbles, given their greatly improved spatial coverage. For reference, this paper also presents two appendices with detailed descriptions of the usage of Fabry–Perot devices, including formulae and explanations for understanding Fabry–Perot observations.
Context.This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to a redshift of one. Intermediate mass galaxies ($M_{\rm J} \leq -20.3$) are ...selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts. Aims.Our primary aim in this study is therefore to obtain a sample of intermediate-mass galaxies with known spectroscopic redshift to be used for further analysis of their 3D-kinematics. We also intend to test whether this important cosmological field may be significantly affected by cosmic variance. Methods.The spectroscopic observations were carried out using VIMOS on the ESO VLT. The data reduction was done using a set of semi-automatic IRAF procedures developed by our team. Results.We have spectroscopically identified 691 objects including 580 galaxies, 7 QSOs, and 104 stars. The overall completeness achieved is about 76% for objects with $I_{AB} \leq 23.5$ in the CDFS after excluding instrumental failures. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large-scale structures in the CDFS, which are found to be more prominent than in other redshift surveys. To test the impact of these structures in the GOODS-South field, we constructed a representative redshift catalog of 640 galaxies with $I_{AB} \leq 23.5$ and $z \leq 1$. We then compared the evolution of rest-frame U, B, V, and K galaxy luminosity densities to the one derived from the Canada France Redshift Survey (CFRS). The GOODS South field shows a significant excess of luminosity densities in the $z = 0.5$–0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 μm. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large-scale structures at $z = 0.668$ and at $z = 0.735$, which contain a significant excess of evolved, massive galaxies when compared to other fields. Conclusions.This leads to a clear warning about the results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities that are apparently less affected by cosmic variance (0.25 dex at 2.1 μm), however, at the cost of any ease in disentangling the evolutionary and cosmic variance effects.
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The contribution of the merging process to the early phase of galaxy assembly at z > 1 and, in particular, to the build-up of the red sequence, still needs to be accurately assessed. We aim to ...measure the major merger rate of star-forming galaxies at 0.9 < z < 1.8, using close pairs identified from integral field spectroscopy (IFS). Merging of star-forming galaxies is frequent at around the peak in star formation activity. Our results show that gasrich mergers make an important contribution to the growth of massive galaxies since z ~1.5, particularly on the build-up of the red sequence.
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We present new Gemini/GMOS spectroscopic and archival imaging data of the interacting galaxy NGC 92, which is part of a compact group and displays an extended tidal tail. We have studied the physical ...properties of 20 star-forming complexes in this system. We found that the star-forming regions located in the tidal tail of NGC 92 have ages younger than ∼8 Myr, which suggests that these objects were formed in situ. The spectroscopic data reveal that these regions have slightly sub-solar metallicities, suggesting that they were formed from pre-enriched material. Using the oxygen abundances derived for each system, we found that the extended tidal tail of NGC 92 has a flat metallicity distribution. Although this scenario is consistent with N-body simulations of interacting systems, where there is gas mixing triggered by the interaction, archival Hα Fabry–Perot data cubes of NGC 92 have not shown a velocity gradient along the tail of this galaxy, which under certain assumptions could be interpreted as a lack of gas flow in the tail. Our results suggest that a fraction of the enriched gas that was originally located in the centre of the galaxy was expelled into the tidal tail when the interacting process that formed the tail happened. However, we cannot exclude the scenario in which the star formation in the tail has increased its original oxygen abundance.
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