Table 5
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The Spitzer Interacting Galaxies Survey is a sample of 103 nearby galaxies in 48 systems, selected using association likelihoods and therefore free from disturbed morphology biases. All galaxies have been observed with Infrared Array Camera and MIPS 24 μm bands from the Spitzer Space Telescope. This catalog presents the global flux densities and co...
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Citations
... References Description SIGS 100 1,2,3 Nearby interacting galaxies presented by Brassington et al. (2015). SB 21 4,5 Galaxies dominated by star-formation. ...
... b We found reliable SEDs in 189 galaxies (see Sect. 5), including the 11 galaxies presented by Dietrich et al. (2018). References: (1) Keel et al. (1985), (2) Lanz et al. (2013Lanz et al. ( , 2014, (3) Brassington et al. (2015), (4) Brandl et al. (2006), (5) Lintott et al. (2008Lintott et al. ( , 2011 and (17) Our AGN sample includes three galaxies from the Great Observatories All-Sky LIRG Survey (GOALS, Stierwalt et al. 2013, a collection of Ultra-Luminous Infrared Galaxies (ULIRGs) with available Spitzer/IRS spectra), that meet our selection criteria: NGC 1068, NGC 7674, and MCG-03-34-63. We also include NGC 4151, a composite AGN/starburst galaxy (Higuera-G. ...
Emission from active galactic nuclei (AGNs) is known to play an important role in the evolution of many galaxies including luminous and ultraluminous systems (U/LIRGs), as well as merging systems. However, the extent, duration, and exact effects of its influence are still imperfectly understood. To assess the impact of AGNs on interacting systems, we present a Spectral Energy Distribution (SED) analysis of a sample of 189 nearby galaxies. We gather and systematically re-reduce archival broad-band imaging mosaics from the ultraviolet to the far-infrared using data from GALEX, SDSS, 2MASS, IRAS, WISE, Spitzer and Herschel. We use spectroscopy from Spitzer/IRS to obtain fluxes from fine-structure lines that trace star formation and AGN activity. Utilizing the SED modelling and fitting tool CIGALE, we derive the physical conditions of the ISM, both in star-forming regions and in nuclear regions dominated by the AGN in these galaxies. We investigate how the star formation rates (SFRs) and the fractional AGN contributions ($f_{\rm{AGN}}$) depend on stellar mass, galaxy type, and merger stage. We find that luminous galaxies more massive than about $10^{10} \rm{M}_{*}$ are likely to deviate significantly from the conventional galaxy main-sequence relation. Interestingly, infrared AGN luminosity and stellar mass in this set of objects are much tighter than SFR and stellar mass. We find that buried AGNs may occupy a locus between bright starbursts and pure AGNs in the $f_{\rm{AGN}}$-[Ne V]/[Ne II] plane. We identify a modest correlation between $f_{\rm{AGN}}$ and mergers in their later stages.
... Moreover, it could also be possible that in these galaxies interactions and mergers are responsible for triggering independently both enhanced Median Q3 AGN 31 48 100 30 56 85 55 85 151 Non-AGN 23 44 72 2 35 56 38 58 91 star formation and AGN activity, as has been shown in previous studies (e.g. Hopkins et al. 2008;Lamastra et al. 2013;Brassington et al. 2015;Hong et al. 2015;Knapen, Cisternas & Querejeta 2015;Dietrich et al. 2018). However, taking into account high SFRs in the rest of AGN sample (e.g. in 26 per cent and 25 per cent of galaxies classified as class 1 and class 2, respectively), and higher obtained SFR values in comparison to non-AGNs independently on morphology (as shown above), suggests that interactions and mergers alone cannot explain the results. ...
This paper studies morphological properties of 103 green valley FIR active and 2609 non-active galaxies presented in Mahoro et al. (2017). The photometric data from the COSMOS survey were used, and the morphological parameters, such as Abraham and Conselice-Bershady concentration indices, Gini, M20 moment of light, and asymmetry, were analysed taking into account public catalogues. Furthermore, a visual classification of galaxies was performed. We found that the fraction of peculiar galaxies with clear signs of interactions and mergers is significantly higher in AGN (38%) than non-AGN (19%) green valley galaxies, while non-AGN galaxies from our sample are predominantly spirals (46%). We found that the largest fraction of our green valley galaxies is located on the main-sequence (MS) of star formation, independently on morphology, which is in contrast with most of previous studies carried out in optical. We also found that FIR AGN green valley galaxies have significantly higher star formation rates in all analysed morphological types. Therefore, our results suggest that interactions and mergers obtained in the high fraction of FIR AGN contribute significantly to high star formation rates observed in the selected sample, but are not the only mechanism responsible for enhancing star formation, and others such as AGN positive feedback could contribute as well. In future we will study in more details the possibility of AGN positive feedback through the spectroscopic analysis of public and our SALT data.
... Finding in this work a larger fraction of disturbed morphologies in 38% of AGN suggests that interactions and mergers play an important role in these active galaxies and could contribute to their higher SFRs. Moreover, it could also be possible that in these galaxies interactions and mergers are responsible for triggering independently both enhanced star formation and AGN activity, as has been shown in previous studies (e.g., Hopkins et al. 2008;Lamastra et al. 2013;Brassington et al. 2015;Hong et al. 2015;Knapen et al. 2015;Dietrich et al. 2018). However, taking into account high SFRs in the rest of AGN sample (e.g., in 26% and 25% of galaxies classified as class 1 and class 2, respectively), and higher obtained SFR values in comparison to non-AGN independently on morphology (as shown above), suggests that interactions and mergers alone cannot explain the results. ...
This paper studies morphological properties of 103 green valley FIR active and 2609 non-active galaxies presented in Mahoro et al. 2017. The photometric data from the COSMOS survey were used, and the morphological parameters, such as Abraham and Conselice-Bershady concentration indices, Gini, M20 moment of light, and asymmetry, were analysed taking into account public catalogues. Furthermore, a visual classification of galaxies was performed. We found that the fraction of peculiar galaxies with clear signs of interactions and mergers is significantly higher in AGN (38%) than non-AGN (19%) green valley galaxies, while non-AGN galaxies from our sample are predominantly spirals (46%). We found that the largest fraction of our green valley galaxies is located on the main-sequence (MS) of star formation, independently on morphology, which is in contrast with most of previous studies carried out in optical. We also found that FIR AGN green valley galaxies have significantly higher star formation rates in all analysed morphological types. Therefore, our results suggest that interactions and mergers obtained in the high fraction of FIR AGN contribute significantly to high star formation rates observed in the selected sample, but are not the only mechanism responsible for enhancing star formation, and others such as AGN positive feedback could contribute as well. In future we will study in more details the possibility of AGN positive feedback through the spectroscopic analysis of public and our SALT data.
... Several works have shown that in the Local Universe, a high star formation rate (SFR) is primarily triggered by interactions or mergers ( Kennicutt et al. 1987;Brassington et al. 2015). Therefore, it can be said that there is a relationship between current or past interactions and the LIRG phenomena. ...
We present scanning Fabry-Perot interferometric observations of CIG 993, which is an apparently isolated luminous infrared galaxy that also exhibits luminous blue compact and Wolf-Rayet galaxy features, and which also has a high star formation rate. Our high-resolution observations of the H emission line allowed us to derive the radial velocity field (VF), the velocity dispersion σ, and the residual VFs of the galaxy. This galaxy exhibits several kinematical components. On the one hand, the velocity gradients detected on the VF can be associated with a rotating disk, which is in contrast to previous results with less spectral resolution. However, the VF, the σ and residual VF show significant deviations from circular motions in the central part of the galaxy that matches a region with high number of Wolf-Rayet and O stars, which is coincident with the blue luminous component of the galaxy. We find narrow and broad velocity components for the ionized gas in the central part of the galaxy. The broad component is evidence of a central outflow related with the ongoing burst of stellar formation. The morpho-kinematical analysis of the galaxy indicates we are only seeing the brightest parts of the galaxy, which correspond to the bulge, a central bar and the beginning of the disk. We believe that CIG 993 is a disk galaxy that harbors important star-forming processes, which are most likely caused by a relatively recent interaction. This could imply that small encounters can change the global characteristics of a galaxy without disturbing the main rotation disk motion or the morphology of the galaxy. © 2018. The American Astronomical Society. All rights reserved..
... In the recent years, the concept of galaxies as isolated stellar systems has proved to be undoubtedly misleading. Grounds for the interaction between "island universes" come from the images of interactions between external galaxies 30 and the streams in the halo of the Milky Way 31 . More recently, it has been suggested that the disk of the Galaxy itself may have suffered from the impact of satellites which left an imprint in the form of velocity gradients, density asymmetries with respect to the mid-plane and planar rings 17,32 . ...
Most of the stars in our Galaxy including our Sun, move in a disk-like component and give the Milky Way its characteristic appearance on the night sky. As in all fields in science, motions can be used to reveal the underlying forces, and in the case of disk stars they provide important diagnostics on the structure and history of the Galaxy. But because of the challenges involved in measuring stellar motions, samples have so far remained limited in their number of stars, precision and spatial extent. This has changed dramatically with the second Data Release of the Gaia mission which has just become available. Here we report that the phase space distribution of stars in the disk of the Milky Way is full of substructure with a variety of morphologies, most of which have never been observed before. This includes shapes such as arches and shells in velocity space, and snail shells and ridges when spatial and velocity coordinates are combined. The nature of these substructures implies that the disk is phase mixing from an out of equilibrium state, and that the Galactic bar and/or spiral structure are strongly affecting the orbits of disk stars. Our analysis of the features leads us to infer that the disk was perturbed between 300 and 900 Myr ago, which matches current estimations of the previous pericentric passage of the Sagittarius dwarf galaxy. The Gaia data challenge the most basic premise of stellar dynamics of dynamical equilibrium, and show that modelling the Galactic disk as a time-independent axisymmetric component is definitively incorrect. These findings mark the start of a new era when, by modelling the richness of phase space substructures, we can determine the gravitational potential of the Galaxy, its time evolution and the characteristics of the perturbers that have most influenced our home in the Universe.
... In Fig. 2 we overlay the location of the discrete sources on a multi-band image consisting of HST images in the F814W (814 nm; green) and F435W (435 nm; blue) and a Spitzer IRAC band 4 (8 µm; red) non-stellar image. The IRAC non stellar image in particular was produced by subtracting a scaled 3.6 µm image from the 8 µm in order to remove the stellar emission (Brassington et al. 2015). The above filters give a picture of the distribution of the old, young, and obscured young stellar populations respectively (Fig. 2). ...
... In addition we constructed a map of specific star formation rate (sSFR; defined as the SFR per unit stellar mass) of Arp 299. We used images in the 8 µm and 3.6 µm obtained from the Spitzer IRAC camera provided by Brassington et al. (2015). We transformed the 8 µm non-stellar image to SFR map using the relation : ...
... We have also calculated the SFR from the polycyclic aromatic hydrocarbon (PAH) emission, which is a reasonably good SFR indicator (Wu et al. 2005;Shipley et al. 2016), using an IRAC 8µm non stellar image (Brassington et al. 2015) and the calibration relation of Wu et al. (2005). This gives SFR8µm = 33.06 ...
We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray
sources with luminosities above ∼4.0 × 1038 erg s−1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete
sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them
as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources.
Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling
relations of X-ray binaries with the star formation rate (SFR). Although the high metalicity of the galaxy could result in
lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant
scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy
shows the presence of a hot gaseous component with kT = 0.72 ± 0.03 keV, contributing ∼20% of the soft (0.1-2.0 keV) unabsorbed
luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find
that the AGN in NGC 3690 contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.
Emission from active galactic nuclei (AGNs) is known to play an important role in the evolution of many galaxies including luminous and ultraluminous systems (U/LIRGs), as well as merging systems. However, the extent, duration, and exact effects of its influence are still imperfectly understood. To assess the impact of AGNs on interacting systems, we present a Spectral Energy Distribution (SED) analysis of a sample of 189 nearby galaxies. We gather and systematically re-reduce archival broad-band imaging mosaics from the ultraviolet to the far-infrared using data from GALEX, SDSS, 2MASS, IRAS, WISE, Spitzer and Herschel. We use spectroscopy from Spitzer/IRS to obtain fluxes from fine-structure lines that trace star formation and AGN activity. Utilizing the SED modelling and fitting tool cigale, we derive the physical conditions of the ISM, both in star-forming regions and in nuclear regions dominated by the AGN in these galaxies. We investigate how the star formation rates (SFRs) and the fractional AGN contributions (fAGN) depend on stellar mass, galaxy type, and merger stage. We find that luminous galaxies more massive than about $10^{10} \rm {M}_{*}$ are likely to deviate significantly from the conventional galaxy main-sequence relation. Interestingly, infrared AGN luminosity and stellar mass in this set of objects are much tighter than SFR and stellar mass. We find that buried AGNs may occupy a locus between bright starbursts and pure AGNs in the fAGN-[Ne v]/[Ne ii] plane. We identify a modest correlation between fAGN and mergers in their later stages.
Context . A moderate enhancement of the star formation rates (SFR) in local interacting galaxies has been reported, but the physical mechanisms leading to this increase are not clear.
Aims . We study the atomic gas content and the central stellar mass concentration for a sample of almost 1500 nearby galaxies to further investigate the nature of starbursts and the influence of galaxy-galaxy interactions on star formation.
Methods . We used a sample of catalogued interacting and non-interacting galaxies in the S ⁴ G survey – along with archival H I gas masses, stellar masses ( M* ), and SFRs from IRAS far-infrared fluxes – and calculate depletion times ( τ ) and gas fractions. We traced the central stellar mass concentration from the inner slope of the stellar component of the rotation curves, dRv* (0). Starbursts are defined as galaxies with a factor > 4 enhanced SFR relative to a control sample of non-interacting galaxies which are ±0.2 dex in stellar mass and ±1 in T -type.
Results . Starbursts are mainly early-type ( T ≲ 5), massive spiral galaxies ( M* ≳ 10 ¹⁰ M⊙ ) that are not necessarily interacting. For a given stellar mass bin, starbursts are characterised by lower gas depletion times, similar gas fractions, and larger central stellar mass concentrations than non-starburst galaxies. The global distributions of gas fraction and gas depletion time of interacting galaxies are not statistically different from those of their non-interacting counterparts. However, in the case of currently merging galaxies, the median gas depletion time is a factor of 0.4 ± 0.2 that of control sample galaxies, and their SFRs are a factor of 1.9 ± 0.5 enhanced, even though the median gas fraction is similar.
Conclusions . Starbursts present long-lasting star formation in circumnuclear regions, which causes an enhancement of the central stellar density at z ≈ 0 in both interacting and non-interacting systems. Starbursts have low gas depletion timescales, yet similar gas fractions as normal main-sequence galaxies. Galaxy mergers cause a moderate enhancement of the star formation efficiency.
Context. Encounters between galaxies modify their morphology, kinematics, and star formation history. The relation between these changes and external perturbations is not straightforward. The great number of parameters involved requires both the study of large samples and individual encounters where particular features, motions, and perturbations can be traced and analysed in detail.
Aims. We analysed the morphology, kinematics, and dynamics of two luminous infrared spiral galaxies of almost equal mass, NGC 5257 and NGC 5258, in which star formation is mostly confined to the spiral arms, in order to understand interactions between galaxies of equivalent masses and star-forming processes during the encounter.
Methods. Using scanning Fabry–Perot interferometry, we studied the contribution of circular and non-circular motions and the response of the ionized gas to external perturbations. We compared the kinematics with direct images and traced the star-forming processes and gravitational effects due to the presence of the other galaxy. The spectral energy distribution of each member of the pair was fitted. A mass model was fitted to the rotation curve of each galaxy.
Results. Large, non-circular motions detected in both galaxies are associated with a bar, spiral arms, and HII regions for the inner parts of the galaxies, and with the tidal interaction for the outer parts of the discs. Bifurcations in the rotation curves indicate that the galaxies have recently undergone pericentric passage. The pattern speed of a perturbation of one of the galaxies is computed. Location of a possible corotation seems to indicate that the gravitational response of the ionized gas in the outer parts of the disc is related to the regions where ongoing star formation is confined. The spectral energy distribution fit indicates slightly different star formation history for each member of the pair. For both galaxies, a pseudo-isothermal halo better fits the global mass distribution.
Galaxy mergers are key events in galaxy evolution, often causing massive starbursts and fueling active galactic nuclei (AGN). In these highly dynamic systems, it is not yet known how much each of these two mechanisms contributes to the total luminosity, at what interaction stages they occur, and how long they persist. Here we estimate the fraction of the bolometric infrared (IR) luminosity that can be attributed to AGNs by measuring and modeling the full ultraviolet to far-infrared spectral energy distributions (SEDs) in up to 33 broad bands for 23 merging galaxies with the Code for Investigating Galaxy Emission. In addition to a sample of 11 confirmed AGN in late-stage mergers, found in the Infrared Array Satellite Revised Bright Galaxy Sample or Faint Source Catalog, our sample includes a comparison sample of 12 early-stage mergers from the $Spitzer$ Interacting Galaxies Survey. We perform identical SED modeling of simulated mergers to validate our methods, and we supplement the SED data with mid-IR spectra of diagnostic lines obtained with $Spitzer$ InfraRed Spectrograph. The estimated AGN contributions to the IR luminosities vary from system to system from 0% up to 93% but are significantly greater in the later-stage, more luminous mergers, consistent with what is known about galaxy evolution and AGN triggering.
