S. Leon

Molecular gas in NUclei of GAlaxies (NUGA). I. The counter-rotating LINER NGC 4826

This paper has been partially funded by the Spanish MCyT under projects DGES/AYA2000-927, ESP2001-4519-PE and ESP2002-01693, and European FEDER funds.

The AMIGA project - I. Optical characterization of the CIG catalog

The AMIGA project (Analysis of the Interstellar Medium of Isolated Galaxies) is compiling a multiwavelength database of isolated galaxies that includes optical (B and Hα), infrared (FIR and NIR) and radio (continuum plus HI and CO lines) properties. It involves a refinement of the pioneering Catalog of Isolated Galaxies. This paper is the first in a series and begins with analysis of the global properties of the nearly redshift-complete CIG with emphasis on the Optical Luminosity Function (OLF) which we compare with other recent estimates of the OLF for a variety of environments. The CIG redshift distribution for n = 956 galaxies re-enforces the evidence for a bimodal structure seen earlier in smaller samples. The peaks at redshift near 1500 and 6000 km s −1 , corresponding respectively to galaxies in the local supercluster and those in more distant large-scale components (particularly Perseus-Pisces). The two peaks in the redshift distribution are superimposed on 50% or more of the sample that is distributed in a much more homogeneous way. The CIG probably represents the most homogeneous local field example that has ever been compiled. Our derivation of the CIG OLF is consistent with other studies of the OLF for lower density environments. This comparison via the Schechter parameter formalization shows that: 1) M ∗ increases with galaxy surface density on the sky and 2) α shows a weaker tendency to do the same. The CIG represents the largest and most complete foundation for studies of isolated galaxies and is likely as close as we can come to a field sample.

The AMIGA sample of isolated galaxies. V. Quantification of the isolation

Context. The AMIGA project aims to build a well defined and statistically significant reference sample of isolated galaxies in order to estimate the environmental effects on the formation and evolution of galaxies. Aims. The goal of this paper is to provide a measure of the environment of the isolated galaxies in the AMIGA sample, quantifying the influence of the candidate neighbours identified in our previous work and their potential effects on the evolution of the primary galaxies. Here we provide a quantification of the isolation degree of the galaxies in this sample. Methods. Our starting sample is the Catalogue of Isolated Galaxies (CIG). We used two parameters to estimate the influence exerted by the neighbour galaxies on the CIG galaxy: the local number density of neighbour galaxies and the tidal strength affecting the CIG galaxy. We show that both parameters together provide a comprehensive picture of the environment. For comparison, those parameters have also been derived for galaxies in denser environments such as triplets, groups and clusters. Results. The CIG galaxies show a continuous spectrum of isolation, as quantified by the two parameters, from very isolated to interacting. The fraction of CIG galaxies whose properties are expected to be influenced by the environment is however low (159 out of 950 galaxies). The isolated parameters derived for the comparison samples gave higher values than for the CIG and we found clear differences for the average values of the 4 samples considered, proving the sensitivity of these parameters. Conclusions. The environment of the galaxies in the CIG has been characterised, using two complementary parameters quantifying the isolation degree, the local number density of the neighbour galaxies and the tidal forces affecting the isolated galaxies. A final catalogue of galaxies has been produced and the most isolated of these galaxies are consequently appropriate to serve as a reference sample for the AMIGA project.

The AMIGA sample of isolated galaxies - IX. Molecular gas properties

Aims. We characterize the molecular gas content (ISM cold phase) using CO emission of a redshift-limited subsample of isolated galaxies from the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project in order to provide a comparison sample for studies of galaxies in different environments. Methods. We present the 12 CO(1–0) data for 273 AMIGA galaxies, most of them (n = 186) from our own observations with the IRAM 30 m and the FCRAO 14 m telescopes and the rest from the literature. We constructed a redshift-limited sample containing galaxies with 1500 km s −1 <v< 5000 km s −1 and excluded objects with morphological evidence of possible interaction. This sample (n = 173) is the basis for our statistical analysis. It contains galaxies with molecular gas masses, MH2 , in the range of ∼10 8 −10 10 M� .I t is dominated, both in absolute number and in detection rate, by spiral galaxies of type T = 3–5 (Sb-Sc). Most galaxies were observed with a single pointing towards their centers. Therefore, we performed an extrapolation to the total molecular gas mass expected in the entire disk based on the assumption of an exponential distribution. We then studied the relationships between MH2 and other galactic properties (LB, D 2 , LK, LFIR ,a ndMHI). Results. We find correlations between MH2 and LB, D 2 , LK ,a ndLFIR. The tightest correlation of MH2 holds with LFIR and, for T = 3– 5, with LK, and the poorest with D 2 . The correlations with LFIR and LK are very close to linearity. The correlation with LB is nonlinear so that MH2 /LB increases with LB. The molecular and the atomic gas masses of our sample show no strong correlation. We find a low mean value, log(MH2 /MHI) = −0.7 (for T = 3–5), and a strong decrease in this ratio with morphological type. The molecular gas column density and the surface density of the star formation rate (the Kennicutt-Schmidt law) show a tight correlation with a rough unity slope. We compare the relations of MH2 with LB and LK found for AMIGA galaxies to samples of interacting galaxies from the literature and find an indication for an enhancement of the molecular gas in interacting galaxies of up to 0.2–0.3 dex.

Gravitational tidal effects on galactic open clusters

We have investigated the 2{D stellar distribution in the outer parts of three nearby open clusters: NGC 2287 (M 41), NGC 2516, and NGC 2548 (M 48). Wide-eld star counts have been performed in two colours on pairs of digitized ESO and SRC Schmidt plates, allowing us to select likely cluster members in the colour-magnitude diagrams. Cluster tidal extensions were emphasized using a wavelet transform. Taking into account observational biases, namely the galaxy clustering and dierential extinction in the Galaxy, we have associated these stellar overdensities with real open cluster structures stretched by the galactic gravitational eld. As predicted by theory and simulations, and despite observational limitations, we detected a general elongated (prolate) shape in a direction parallel to the galactic Plane, combined with tidal tails extended perpendicularly to it. This geometry is due both to the static galactic tidal eld and the heating up of the stellar system when crossing the Disk. The time varying tidal eld will deeply aect the cluster dynamical evolution, and we emphasize the importance of adiabatic heating during the Disk-shocking. In the case of NGC 2548, our dating of the last shocking with the Plane (based on a tidal clump) is consistent with its velocity. During the 10{20 Z-oscillations experienced by a cluster before its dissolution in the Galaxy, crossings through the galactic Disk contribute to at least 15% of the total mass loss. Using recent age estimations published for open clusters, we nd a destruction time-scale of about 600 Myr for clusters in the solar neighbourhood.

The AMIGA sample of isolated galaxies III. IRAS data and infrared diagnostics

Aims. We describe the mid- (MIR) and far- (FIR) infrared properties of a large (∼1000) sample of the most isolated galaxies in the local Universe. This sample is intended as a “nurture-free” zero point against which more environmentally influenced samples can be compared. Methods. We reprocess IRAS MIR/FIR survey data using the ADDSCAN/SCANPI utility for 1030 out of 1050 galaxies from the Catalogue of Isolated Galaxies (CIG) as part of the AMIGA project. We focus on diagnostics (FIR luminosity LFIR, R = log(LFIR/LB), and IRAS colours) thought to be sensitive to effects of environment or interaction. Results. The distribution of log(LFIR) sharply peaks from 9.0–10.5, with very few (<2%) galaxies above 10.5. Review of available optical images of the most FIR luminous galaxies finds the majority likely to be interacting systems missed in our earlier morphological reevaluation. The optically normalised luminosity diagnostic R = log(LFIR/LB) shows a sharply peaked distribution between 0.0 and −1.0. These results were compared to the magnitude limited sample of the Center for Astrophysics that was selected without environmental discrimination. This modestly (e.g., compared to cluster, binary galaxy, and compact group samples) environmentally affected sample shows a significantly higher mean log(LFIR), and R, whereas the mean log(LB) is the same. Our sample shows a strong LFIR vs. LB correlation, with a slope steeper than one (LFIR ∝ L 1.41 B ). Interacting galaxies were found above this correlation, showing an enhancement in LFIR. With respect to the IRAS colours, we found higher F60/F100 values for ellipticals and late-type galaxies than for spirals, indicating a higher dust temperature. The mean value of F60/F100 was found to be lower than for interacting samples from the literature. Conclusions. The results indicate that the FIR emission is a variable enhanced by interaction, and that our sample probably shows the lowest possible mean value. This attests to the utility of our sample for defining a nurture-free zero point.

The AMIGA sample of isolated galaxies - II. Morphological refinement

Received / accepted Abstract. We present a complete refinement of the optical morphologies for galaxies in the Catalog of Isolated Galaxies (Karachentseva 1973) that forms the basis of the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project. Uniform reclassification using the digitized POSS II benefit ed from the high resolution and dynamic range of that sky survey. Comparison with independent classifications made for an SDS S overlap sample of more than 200 galaxies confirms the reli- ability of the early vs. late-type discrimination and the ac curacy of spiral subtypes withinT = 1-2. CCD images taken at the Observatorio de Sierra Nevada were also used to solve ambiguities in early versus late-type classifications. A consi derable number of galaxies in the catalog (n = 193) are flagged for the presence of nearby companions or sign s of distortion likely due to interaction. This most isolated sample of galaxies in the local Universe is dominated by two populations: 1) 82% spirals (Sa-Sd) with the bulk being luminous systems with small bulges (63% between types Sb-Sc) and 2) a significant population o f early-type E-S0 galaxies (14%). Most of the types later than Sd are low luminosity galaxies concentrated in the local superclus- ter where isolation is diffi cult to evaluate. The late-type spiral majority of the sampl e spans a luminosity range MB−corr =−18 to −22 mag. Few of the E/S0 population are more luminous than−21.0 marking an absence of, an often sought, super L ∗ merger (e.g. fossil elliptical) population. The rarity of high lum inosity systems results in a fainter derived M ∗ for this population com- pared to the spiral optical luminosity function (OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending how the sample is defined. This marks the AMIGA sample as almost unique among samples that compare early and late-type OLFs sep- arately. In other samples, which always involve galaxies in higher density environments, M ∗/S0 is almost always 0.3-0.5 mag brighter than M ∗, presumably reflecting a stronger correlation between M ∗ and environmental density for early-type galaxies.

Molecular gas in NUclei of GAlaxies (NUGA) - II. The ringed LINER NGC 7217

S. L. is supported by a Marie Curie Individual Fellowship contract HPMF-CT-20002-01734 from the European Union.

Molecular gas in NUclei of GAlaxies (NUGA) VII. NGC 4569, a large scale bar funnelling gas into the nuclear region ⋆

This work is part of the NUGA survey of CO emission in nearby active galaxies. We present observations of NGC 4569, a member of the Virgo Cluster. We analyse the molecular gas distribution and kinematics in the central region and we investigate a possible link to the strong starburst present at the nucleus. 70% of the (1.1 ± 0.2) × 10 9 Mof molecular gas detected in the inner 20 �� is found to be concentrated within the inner 800 pc and is distributed along the large scale stellar bar seen in near-infrared observations. A hole in the CO distribution coincides with the nucleus where most of the Hα emission and blue light are emitted. The kinematics are modelled in three different ways, ranging from the purely geometrical to the most physical. This approach allows us to constrain progressively the physical properties of the galaxy and eventually to emerge with a reasonable fit to an analytical model of orbits in a barred potential. Fitting an axisymmetric model shows that the non-circular motions must be comparable in amplitude to the circular motions (120 km s −1 ). Fitting a model based on elliptical orbits allows us to identify with confidence the single inner Lindblad resonance (ILR) of the large scale bar. Finally, a model based on analytical solutions for the gas particle orbits in a weakly barred potential constrained by the ILR radius reproduces the observations well. The mass inflow rate is then estimated and discussed based on the best fit model solution. The gravitational torques implied by this model are able to efficiently funnel the gas inside the ILR down to 300 pc, although another mechanism must take over to fuel the nuclear starburst inside 100 pc.

Molecular gas in NUclei of GAlaxies (NUGA) - III. The warped LINER NGC 3718

The research presented in this paper has been financially supported in part by the SFB 494. Stephane Leon is partially supported by DGI Grant AYA 2002-03338 and Junta de Andalucia.