We present the results of the one-year long observational campaign of the type II plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the Whirlpool galaxy). This extensive data set ...makes SN 2005cs the best observed low-luminosity, 56Ni-poor type II plateau event so far and one of the best core-collapse supernovae ever. The optical and near-infrared spectra show narrow P-Cygni lines characteristic of this SN family, which are indicative of a very low expansion velocity (about 1000 km s−1) of the ejected material. The optical light curves cover both the plateau phase and the late-time radioactive tail, until about 380 d after core-collapse. Numerous unfiltered observations obtained by amateur astronomers give us the rare opportunity to monitor the fast rise to maximum light, lasting about 2 d. In addition to optical observations, we also present near-infrared light curves that (together with already published ultraviolet observations) allow us to construct for the first time a reliable bolometric light curve for an object of this class. Finally, comparing the observed data with those derived from a semi-analytic model, we infer for SN 2005cs a 56Ni mass of about 3 × 10−3 M⊙, a total ejected mass of 8–13 M⊙ and an explosion energy of about 3 × 1050 erg.
We present an analysis of the stellar mass growth over the last 10 Gyr ($z\le 2$) using a unique large sample of galaxies selected at $3.6~\mu$m. We have assembled accurate photometric and ...spectroscopic redshifts for ~21 200 and 1500 galaxies, respectively, with F(3.6 μm) ≥ 9.0 μJy by combining data from Spitzer-SWIRE IRAC, the VIMOS VLT Deep Survey (VVDS), UKIDSS and very deep optical CFHTLS photometry. We split our sample into quiescent (red) and active (blue) galaxies on the basis of an SED fitting procedure that we have compared with the strong rest-frame color bimodality $(NUV-r')_{\rm ABS}$. The present sample contains ~ 4400 quiescent galaxies. Our measurements of the K-rest frame luminosity function and luminosity density evolution support the idea that a large fraction of galaxies is already assembled at z ~ 1.2, with almost 80% and 50% of the active and quiescent populations already in place, respectively. Based on the analysis of the evolution of the stellar mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the stellar mass density for the entire sample. We find that the global evolution of the stellar mass density is well reproduced by the star formation rate derived from UV based measurements when an appropriate dust correction is applied, which supports the idea of an initial mass function that is on average universal. Over the last 8 Gyr (z ≤ 1.2) we observe that the stellar mass density of the active population shows a modest mass growth rate ($\dot{\rho}$ ~ 0.005(±0.005) $M_{\odot}$/Mpc3/yr), consistent with a constant stellar mass density, $\rho_{\star}^{\rm active}$ ~ 3.1 $\times$ 108 $M_{\odot}$/Mpc3. In contrast, an increase by a factor of ~2 for the quiescent population over the same timescale is observed. As a consequence, the growth of the stellar mass in the quiescent population must be due to the shutoff of star formation in active galaxies that migrate into the quiescent population. We estimate this stellar mass flux to be $\dot{\rho}_{A\rightarrow Q}$ ~ 0.017(±0.004) $M_{\odot}$/Mpc3/yr, which balances the major fraction of new stars born according to our best SFR estimate ($\dot{\rho}$ = 0.025(±0.003) $M_{\odot}$/Mpc3/yr). From $z = 2$ to $z = 1.2$, we observe a major build-up of the quiescent population with an increase by a factor of ~10 in stellar mass (a mass growth rate of ~ 0.063 $M_{\odot}$/Mpc3/yr). This rapid evolution suggests that we are observing the epoch when, for the first time in the history of the universe, an increasing fraction of galaxies end their star formation activity and start to build up the red sequence.
We report the serendipitous detection of a significant overdensity of Herschel-Spectral and Photometric Imaging Receiver 250 μm sources in the vicinity of MRC 1138−26. We use an adaptive kernel ...density estimate to quantify the significance, including a comparison with other fields. The overdensity has a size of ∼3.5-4 arcmin and stands out at ∼5σ with respect to the background estimate. No features with similar significance were found in four Herschel-observed extragalactic control fields: GOODS-North, Lockman, COSMOS and UDS. The chance of having a similar overdensity in a field with the same number but randomly distributed sources is less than 2 per cent. The clump is also visible as a low-surface-brightness feature in the Planck 857 GHz map. We detect 76 sources at 250 μm (with a signal-to-noise ratio greater than 3), in a region of 4 arcmin radius (or 1.51 ± 0.17 arcmin−2); 43 of those (or 0.86 ± 0.13 arcmin−2) are above a flux density limit of 20 mJy. This is a factor of 3.6 in excess over the average 0.24 ± 0.02 arcmin−2 in the four control fields, considering only the sources above 20 mJy. We also find an excess in the number counts of sources with 250 μm flux densities between 30 and 40 mJy, compared to deep extragalactic blank-field number counts. Assuming a fixed dust temperature (30 K) and emissivity (β = 1.5), a crude, blackbody-derived redshift distribution, z
BB, of the detected sources is significantly different from the distributions in the control fields and exhibits a significant peak at z
BB 1.5, although the actual peak redshift is highly degenerate with the temperature. We tentatively suggest, based on z
BB and the similar S250/S350 colours of the sources within the peak, that a significant fraction of the sources in the clump may be at a similar redshift. Since the overdensity lies ∼ 7 arcmin south of the z = 2.16 Spiderweb protocluster MRC 1138−26, an intriguing possibility (that is presently unverifiable given the data in hand) is that it lies within the same large-scale structure.
Aims. We present a homogeneous and complete catalogue of optical galaxy groups identified in the purely flux-limited (17.5 ≤ IAB ≤ 24.0) VIMOS-VLT deep redshift Survey (VVDS). Methods. We use mock ...catalogues extracted from the Millennium Simulation, to correct for potential systematics that might affect the overall distribution as well as the individual properties of the identified systems. Simulated samples allow us to forecast the number and properties of groups that can be potentially found in a survey with VVDS-like selection functions. We use them to correct for the expected incompleteness and, to asses in addition, how well galaxy redshifts trace the line-of-sight velocity dispersion of the underlying mass overdensity. In particular, on these mock catalogues we train the adopted group-finding technique i.e., the Voronoi-Delaunay Method (VDM). The goal is to fine-tune its free parameters, recover in a robust and unbiased way the redshift and velocity dispersion distributions of groups (n(z) and n(σ), respectively), and maximize, at the same time, the level of completeness and purity of the group catalogue. Results. We identify 318 VVDS groups with at least 2 members in the range 0.2 ≤ z ≤ 1.0, among which 144 (/30) with at least 3 (/5) members. The sample has an overall completeness of ~60% and a purity of ~50%. Nearly 45% of the groups with at least 3 members are still recovered if we run the algorithm with a particular parameter set that maximizes the purity (~75%) of the resulting catalogue. We use the group sample to explore the redshift evolution of the fraction fb of blue galaxies (U–B ≤ 1) in the redshift range 0.2 ≤ z ≤ 1. We find that the fraction of blue galaxies is significantly lower in groups than in the global population (i.e. in the whole ensemble of galaxies irrespective of their environment). Both of these quantities increase with redshift, the fraction of blue galaxies in groups exhibiting a marginally significant steeper increase. We also investigate the dependence of fb on group richness: not only we confirm that, at any redshift, the blue fraction decreases in systems with increasing richness, but we find that this result continues to hold towards fainter luminosities.
Aims. It has been widely recognized that processes taking place inside group environment could be important drivers of galaxy evolution. Compact groups of galaxies in particular are excellent ...laboratories for studying galaxy interactions and their effects on the evolution of galaxies due to their high density and low velocity dispersion. SCG0018-4854 is a remarkably high galaxy density and low velocity dispersion group with evidence of a recent interaction. It has been detected and analyzed at different wavelengths, but its kinematics have never been studied in detail. Methods. We obtained VLT FORS2 optical observations and present spectroscopic and photometric evidence to illustrate how dramatically galaxy interactions have affected each of the four group member galaxies. Results. For each galaxy, we detected peculiar kinematics and evidence of recent star formation. In particular, the gas and stellar radial velocity curves of two galaxies are irregular with a level of asymmetry similar to that of other interacting galaxies. We discovered a bar inside NGC 92 thereby revising a previous morphological classification, and we obtained spectroscopic confirmation of the galactic-scale outflow within NGC 89. Conclusions. The peculiar kinematics and dynamical considerations provide a rough estimate of the age of the latest interaction of τ ≈ 0.2-0.7 Gyr, suggesting that SCG0018-4854 is a young and dynamical group.
Aims. We present the low frequency (610 MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. Methods. We use new deep ( {\rm ...rms}\simeq 50 similar to \muJy/beam) observations of the VVDS-VLA field obtained at 610 MHz with the GMRT and matched in resolution (6 arcsec) with already available VLA data at 1.4 GHz on the same field. Results. We find evidence of a change of the dominant population of radio sources below 0.5 mJy (at 1.4 GHz) : between 0.15 and 0.5 mJy the median spectral index is significantly flatter ( \alpha=-0.46\pm 0.03) than that of brighter sources ( \alpha=-0.67\pm 0.05). A relevant contribution below 0.5 mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15 mJy at 1.4 GHz, the median spectral index steepens again ( \alpha=-0.61\pm 0.04) suggesting that the contribution of starburst galaxies becomes important below \sim 0.2 mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects.
Aims. Compact groups of galaxies are excellent laboratories for studying galaxy interactions and their effects on the evolution of galaxies. In particular, dynamically young systems, with a large ...fraction of interacting, late type galaxies, have so far escaped proper studies in the X-ray band and their hot intergalactic medium properties are virtually unknown. Motivated by this lack of knowledge, we present a detailed investigation here of the X-ray properties of such a dynamically young system. Methods. We obtained XMM-Newton observations of one spiral-only system in the new southern compact group catalogue: SCG0018-4854. We present here the results of the data analysis and discuss them in comparison with the few other similar systems also studied in the X-ray band. Results. The 4 members of SCG0018-4854 emit at a level comparable to what is expected based on their optical properties. We detect the low level diffuse emission between galaxies, which is most likely due to the presence of the intergalactic medium. Compared to other spiral–only groups, SCG0018-4854 could be the coolest system detected so far, although the measurements have large uncertainties. These results indicate that high quality deep X-ray observations are needed to allow a proper study of the properties of the potential well of dynamically young systems, before more general conclusions can be drawn on their average characteristics.
Aims. We study a new broad, well-defined arc of optical nebulosity close to the cloud-shock interacting Criss-Cross nebula, derive the basic physical properties of the nebulosity, and revise those of ...the nebula, and compare both objects to simulations of cloud-shock interactions from the literature. Methods. Deep optical, partly wide-field images were used to reveal the intricate morphology and overall extent of the nebulosities. Optical spectroscopy enabled us to uncover their nature. Results. The two nebulosities are obviously physically linked, but are of different types; the Criss-Cross nebula is, as was also shown in an earlier paper, excited via a slow shock from the expanding Orion-Eridanus bubble, but the broad arc is definitely photo-ionised. The source for ionising photons appears to be hot gas in this bubble. Some results of simulations of interactions of SNRs with interstellar clouds available from the literature bear a striking resemblance to our nebulae, which appear to represent an example-unrivalled in closeness and clarity-of an early-to-medium stage in the destruction of an isolated cloud over-run by a highly evolved SNR. Thereby the Criss-Cross nebula is, when seen from the SNR, the rear disrupted part of the original, small cloud, whereas the arc is probably its still rather intact front part.
The Monogem Ring is a huge bright soft X-ray enhancement with a diameter of ~25°. This 0.3 kpc distant structure is a peculiar Galactic supernova remnant in that it is obviously visible only in ...X-rays, due to its expansion into a region of extremely low ambient density: hence, practically no optical emission or a neutral $\ion{H}{i}$ shell was expected to be detectable. Here we report on the discovery of a very faint arc-like nebula on a POSS II R film copy, at the south-eastern borders of the MR. Spectroscopy revealed this filament to have a very large $\ion{S}{ii}$λ 6716+6731/Hα ratio of up to ~1.8, indicating shock excitation, and a low density of Ne < 100 cm-3. There is no hint of $\ion{O}{iii}$ emission in the spectra. On deep wide-field direct images in Hα and in $\ion{S}{ii}$ the nebula appears as a ~20´ long, thin (~1´), structured filament, stretching N-S. We believe that this filament belongs to the MR and became visible due to the interaction of the expanding remnant with a mild density increase in the interstellar medium. Only one other possible optical filament of the MR has been reported in the literature, but no spectrum was provided.
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