Chemo-photometric Implementation Research Articles

Insights into the Evolution of Five Isolated Galaxies

Abstract Galaxy evolution is believed to be conditioned by the environment. Isolated galaxies or galaxies in poor groups are an excellent laboratory to study evolutionary mechanisms where effects of the environment are minimal. We present new Swift-UVOT data in six filters, three in the ultraviolet (UV), of five isolated galaxies aiming at shedding light into their evolution. For all of our targets, we present new UV integrated fluxes, and for some of them also new UBV magnitudes. Our observations allow us to improve their multiwavelength spectral energy distributions, extending them over about three orders of magnitude in wavelength. We exploit our smooth particle hydrodynamical simulations with chemo-photometric implementation anchored, a posteriori, to the global multiwavelength properties of our targets, to give insight into their evolution. Then we compare their evolutionary properties with those previously derived for several galaxies in groups. The evolution of our targets is driven by a merger that occurred several gigayears ago, in the redshift range 0.5 ≤ z ≤ 4.5, not unlike what we have already found for galaxies in groups. The merger shapes the potential well where the gas is accreting, driving the star formation rate and the galaxy evolution. Isolated galaxies should not have suffered from interactions for at least 3 Gyr. However, the initial merger is still leaving its signature on the properties of our targets. Several rejuvenation episodes, triggered by in situ accretion, are highlighted. Moreover, jellyfish morphologies appear as these galaxies achieve their maximum star formation rate, before their quenching phase.

Investigating Early-type Galaxy Evolution with a Multiwavelength Approach. III. Insights from SPH Simulations with Chemophotometric Implementation

We are exploring galaxy evolution in low density environments exploiting smooth particle hydrodynamic simulations including chemo-photometric implementation. From a large grid of simulations of galaxy encounters and mergers starting from triaxial halos of gas e dark matter, we single out the simulations matching the global properties of our targets. These simulations are used to give insights into their evolution. We focus on 11 early-type galaxies selected because of their nearly passive stage of evolution in the nuclear region. However, a variety of UV features are detected in more than half of these galaxies. We find no significant differences in the formation mechanisms between galaxies with or without UV features. Major and minor mergers are able to reproduce their peculiar UV morphologies, galaxy encounters are more suitable for 'normal' early-type galaxies. Their star formation rate self-quenches several Gyr later the merger/encounter occurred, via gas exhaustion and stellar feedback, moving the galaxy from blue to red colors, driving the galaxy transformation. The length of the quenching is mass dependent and lasts from 1 to 5 Gyr or more in the less massive systems. All our targets are gas rich at redshift 1. Three of them assembled at most 40% of their current stellar mass at z>1, and seven assembled more than 50% between redshift 0.5 and 1. Their stellar mass grows with 4% by crossing the Green Valley before reaching their current position on the NUV-r vs. Mr diagram.

Galaxy evolution in groups

Context. Local Group (LG) analogs (LGAs) are galaxy associations dominated by a few bright spirals reminiscent of the LG. The NGC 3447/NGC 3447A system is a member of the LGG 225 group, a nearby LGA. This system is considered a physical pair composed of an intermediate-luminosity late-type spiral, NGC 3447 itself, and an irregular companion, NGC 3447A, linked by a faint, short filament of matter. A ring-like structure in the NGC 3447 outskirts has been emphasised by Galaxy Evolution Explorer (GALEX) observations. Aims. This work aims to contribute to the study of galaxy evolution in low-density environments, a favourable habitat to highly effective encounters, shedding light on the evolution of the NGC 3447/NGC 3447A system. Methods. We performed a multi-λ analysis of the surface photometry of this system to derive its spectral energy distribution and structural properties using ultraviolet (UV), Swift UVOT, and optical Sloan Digital Sky Survey (SDSS) images complemented with available far-IR observations. We also characterised the velocity field of the pair using two-dimensional Hα kinematical observations of the system obtained with PUMA Fabry-Perot interferometer at the 2.1 m telescope of San Pedro Mártir (Mexico). All these data are used to constrain smooth particle hydrodynamic simulations with chemo-photometric implementation to shed light on the evolution of this system. Results. The luminosity profiles, from UV to optical wavelengths, are all consistent with the presence of a disc extending and including NGC 3447A. The overall velocity field does not emphasise any significant rotation pattern, rather a small velocity gradient between NGC 3447 and NGC 3447A. Our simulation, detached from a large grid explored to best-fit the global properties of the system, suggests that this arises from an encounter between two halos of equal mass. Conclusions. NGC 3447 and NGC 3447A belong to the same halo, NGC 3447A being a substructure of the same disk including NGC 3447. The halo gravitational instability, enhanced by the encounter, fuels a long-lived instability in this dark-matter-dominated disk, driving the observed morphology. The NGC 3447/NGC 3447A system may warn of a new class of “false pairs” and the potential danger of a misunderstanding of such objects in pair surveys that could produce a severe underestimate of the total mass of a system.

The NGC 454 system: anatomy of a mixed ongoing merger

This paper focuses on NGC 454, a nearby interacting pair of galaxies (AM0112-554, RR23), composed of an early-type (NGC 454 E) and a star forming late-type companion (NGC 454 W). We aim at characterizing this wet merger candidate via a multi-lambda analysis, from near-UV to optical using SWIFT-UVOT, and mapping the Halpha intensity (I) distribution, velocity (Vr), and velocity dispersion (sigma) fields with SAM+Perot-Fabry at SOAR observations. Luminosity profiles suggest that NGC 454 E is an S0. Distortions in its outskirts caused by the on-going interaction are visible in both optical and near-UV frames. In NGC 454 W, the NUV-UVOT images and the Halpha show a set of star forming complexes connected by a faint tail. Halpha emission is detected along the line connecting NGC 454 E to the NGC 454 main HII complex. We investigate the (I-sigma), (I-Vr ) (Vr-sigma) diagnostic diagrams of the HII complexes, most of which can be interpreted in a framework of expanding bubbles. In the main HII complex, enclosed in the UV brightest region, the gas velocity dispersion is highly supersonic reaching 60 km/s. However, Halpha emission profiles are mostly asymmetric indicating the presence of multiple components with an irregular kinematics. Observations point towards an advanced stage of the encounter. Our SPH simulations with chemophotometric implementation suggest that this mixed pair can be understood in terms of a 1:1 gas/halos encounter giving rise to a merger in about 0.2 Gyr from the present stage.

The evolution of S0s with UV bright rings A SWIFT-UVOT study

AbstractWe report about an ongoing study of the evolution of 24 S0s with UV-bright ring/arm-like structures observed with SWIFT-UVOT and interpreted via SPH simulations with chemo-photometric implementation.

UGC 7639: A Dwarf Galaxy in the Canes Venatici I Cloud

We want to get insight into the formation mechanism and the evolution of UGC 7639, a dwarf galaxy in the Canes Venatici I Cloud (CVnIC). We used archival multiwavelength data to constrain its global properties. Ultraviolet images show that UGC 7639 inner regions are composed mostly by young stellar populations. In addition, we used smoothed particle hydrodynamics simulations with chemophotometric implementation to account for its formation and evolution. UGC 7639 is an example of blue dwarf galaxy whose global properties are well matched by our multiwavelength approach, that is, a suitable approach to highlight the evolution also of these galaxies as a class. We found that the global properties of UGC 7639, namely, its total absolute B-band magnitude, its whole spectral energy distribution, and morphology, are well matched by an encounter with a system four times more massive than our target. Moreover, the current star formation rate of the simulated dwarf, ≈0.03 M⊙ yr−1, is in good agreement with our UV-based estimate. We derived a galaxy age of 8.6 Gyr. Following our simulation, the ongoing star formation will extinguish within 1.6 Gyr, thus leaving a red dwarf galaxy.

The UV window on counter rotating ETGs: insight from SPH simulations with chemo-photometric implementation

The Galaxy Evolution Explorer (GALEX) detected ultraviolet emission in about 50 % of multi-spin early-type galaxies (ETGs), suggesting the occurrence of a recent rejuvenation episode connected to the formation of these kinematical features. With the aim at investigating the complex evolutionary scenario leading to the formation of counter rotating ETGs (CR-ETGs) we use our Smooth Particle Hydrodynamic (SPH) code with chemo-photometric implementation. We discuss here the UV evolutionary path of two CR-ETGs, NGC 3593 and NGC 5173, concurrently best fitting their global observed properties, i.e., morphology, dynamics, as well as their total B-band absolute magnitude and spectral energy distribution (SED) extended over three orders of magnitude in wavelength. These simulations correspond to our predictions about the target evolution which we follow in the color-magnitude diagram (CMD), near-UV (NUV) versus r-band absolute magnitude, as a powerful diagnostic tool to emphasize rejuvenation episodes.

THENUV–rVERSUSMrPLANE AS A TRACER OF EARLY-TYPE GALAXY EVOLUTION IN THE USGC U376 AND LGG 225 GROUPS

With the aim of tracing back the evolution of galaxies in nearby groups we use smooth particle hydrodynamical (SPH) simulations with chemo-photometric implementation. Here we focus on the evolution of the early-type members (Es and S0s, ETGs hereafter) in two groups, USGC U376 and LGG 225, both in the Leo cloud. We use the near-UV (NUV)-optical rest-frame $NUV-r$ versus $M_r$ color magnitude diagram to follow their evolution, from the blue cloud (BC) to the red sequence (RS), through the green valley (GV). ETGs brighter than $M_r=-21$ mag are older than 13 Gyr and spend up to 10 Gyr of their overall evolutionary time in the BC before they reach the RS migrating through the GV. Fainter ETGs are younger, of about 2 Gyr on average, and evolve for about 7-8 Gyr along the BC. The turn-off occurs at z ~ 0.3-0.4. Therefore these ETGs spend up to 3-5 Gyr crossing the GV; UGC 06324, the faintest ETG in the sample, still is in the GV. The mechanism driving their evolution is gravitational, due to merging and/or interaction. Our SPH simulations suggest that ETG members of these groups evolved toward the RS before and during the group collapse phase. This result is consistent with the dynamical analysis of both groups showing that they are not yet virialized.

Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud

With the aim of investigating galaxy evolution in nearby galaxy groups, we analyzed the spectral energy distribution of 24 galaxies, members of two groups in the Leo cloud, USGC U268 and USGC U376. We estimated the ages and stellar masses of the galaxies by fitting their total apparent magnitudes from far-ultraviolet to near-infrared with population synthesis models. The comparison of the results for a subsample of galaxies with smooth particle hydrodynamic (SPH) simulations with chemo-photometric implementation, shows that in most cases the estimated stellar masses obtained with the two different approaches are in good agreement. The kinematical and dynamical analysis indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is likely in a more evolved phase towards virialization.

Catching spiral – S0 transition in groups. Insights from SPH simulations with chemo-photometric implementation

We are investigating the co-evolution of galaxies within groups combining multi-wavelength photometric and 2D kinematical observations. Here we focus on S0s showing star formation in ring/arm-like structures. We use smooth particle hydrodynamical simulations (SPH) with chemo-photometric implementation which provide dynamical and morphological information together with the spectral energy distribution (SED) at each evolutionary stage. As test cases, we simulate the evolution of two such S0s: NGC 1533 and NGC 3626.The merging of two halos with mass ratio 2:1, initially just composed of DM and gas, well match their observed SEDs, their surface brightness profiles and their overall kinematics. The residual star formation today “rejuvenating” the ring/arm like structures in these S0s is then a mere consequence of a major merger, i.e. this is a phase during the merger episode. The peculiar kinematical features, e.g. gas-stars counter rotation in NGC 3626, depends on the halos initial impact parameters. Furthermore, our simulations allow to follow, in a fully consistent way, the transition of these S0s through the green valley in the NUV-r vs. Mr colour magnitude diagram, which they cross in about 3–5Gyrs, before reaching their current position in the red sequence. We conclude that a viable mechanism driving the evolution of S0s in groups is of gravitational origin.

Insight into the evolution of the innermost region of the NGC 1023 Group

The NGC 1023 group is one of the most studied nearby groups. Our aim is to give an insight into the evolution of its innermost region by means of ultraviolet observations and proper models. We use far-ultraviolet and near-ultraviolet GALEX archival data as well as a large set of smoothed particle hydrodynamics simulations with chemo-photometric implementation. From the UV observations we find that several, already known, dwarf galaxies very close to NGC 1023 are also detected in the ultraviolet and two more objects (with no optical counterpart) can be added to the group. Using these data, we construct exhaustive models to account for their formation. We find that the whole spectral energy distribution of NGC 1023 and its global properties are well matched by a simulation that provides a minor merger with a companion system 5 times less massive. The strong interaction phase started 7.7 Gyr ago and the final merger 1.8 Gyr ago.