Relations among structural parameters in barred galaxies with a direct measurement of bar pattern speed

We investigate the relations between the properties of bars and their host galaxies in a sample of 77 nearby barred galaxies, spanning a wide range of morphological types and luminosities, with 34 SB0-SBa and 43 SBab-SBc galaxies. The sample includes all the galaxies with reliable direct measurement of their bar pattern speed based on long-slit or integral-field stellar spectroscopy using the Tremaine-Weinberg method. We limited our analysis to the galaxies with a relatively small relative error on the bar pattern speed (smaller than 50 per cent) and not hosting an ultrafast bar. For each galaxy, we collected the radius, strength, pattern speed, corotation radius, and rotation rate for the bar and we also collected the Hubble type and absolute SDSS r-band magnitude. We also used literature bulge-to-total luminosity ratio for a subsample of 53 galaxies with an available photometric decomposition. We confirmed earlier observational findings that longer bars rotate with lower bar pattern speeds, shorter bars are weaker, and bars with a small bar rotation rate rotate with higher bar pattern speeds and have smaller corotation radii. In addition, we found that stronger bars rotate with lower bar pattern speeds, as predicted from the interchange of angular momentum during bar evolution, which in turn may depend on different galaxy properties. Moreover, we report that brighter galaxies host longer bars, which rotate with lower bar pattern speeds and have larger corotation radii. This result is in agreement with a scenario of downsizing in bar formation, if more massive galaxies formed earlier and had sufficient time to slow down, grow in length, and push corotation outwards.Comment: revised and accepted for pubblication in Astronomy & Astrophysic

Bar pattern speeds in CALIFA galaxies

Context. About 35% of the nearby disc galaxies host a weak bar for which different formation scenarios, including the weakening of a strong bar and tidal interaction with a companion, have been suggested. Measuring the bar pattern speeds of a sample of weakly barred galaxies is a key step in constraining their formation process, but such a systematic investigation is still missing. Aims. We investigated the formation process of weak bars by measuring their properties in a sample of 29 nearby weakly barred galaxies, spanning a wide range of morphological types and luminosities. The sample galaxies were selected to have an intermediate inclination, a bar at an intermediate angle between the disc minor and major axes, and an undisturbed morphology and kinematics to allow the direct measurement of the bar pattern speed. Combining our analysis with previous studies, we compared the properties of weak and strong bars. Methods. We measured the bar radius and strength from the r band images available in the Sloan Digital Sky Survey and bar pattern speed and corotation radius from the stellar kinematics obtained by the Calar Alto Legacy Integral Field Area Survey. We derived the bar rotation rate as the ratio between the corotation and bar radii. Results. Thirteen out of 29 galaxies (45%), which were morphologically classified as weakly barred from a visual inspection, do not actually host a bar component or their central elongated component is not in rigid rotation. We successfully derived the bar pattern speed in 16 objects. Two of them host an ultrafast bar. Using the bar strength to differentiate between weak and strong bars, we found that the weakly barred galaxies host shorter bars with smaller corotation radii than their strongly barred counterparts. Weak and strong bars have similar bar pattern speeds and rotation rates, which are all consistent with being fast. We did not observe any difference between the bulge prominence in weakly and strongly barred galaxies, whereas nearly all the weak bars reside in the disc inner parts, contrary to strong bars. Conclusions. We ruled out that the bar weakening is only related to the bulge prominence and that the formation of weak bars is triggered by the tidal interaction with a companion. Our observational results suggest that weak bars may be evolved systems exchanging less angular momentum with other galactic components than strong bars

Testing for relics of past strong buckling events in edge-on galaxies: Simulation predictions and data from S4G

The short-lived buckling instability is responsible for the formation of at least some box/peanut (B/P) shaped bulges, which are observed in most massive, z = 0, barred galaxies. Nevertheless, it has also been suggested that B/P bulges form via the slow trapping of stars onto vertically extended resonant orbits. The key difference between these two scenarios is that when the bar buckles, symmetry about the mid-plane is broken for a period of time. We use a suite of simulations (with and without gas) to show that when the buckling is sufficiently strong, a residual mid-plane asymmetry persists for several Gyrs after the end of the buckling phase, and is visible in simulation images. On the other hand, images of B/P bulges formed through resonant trapping and/or weak buckling remain symmetric about the mid-plane. We develop two related diagnostics to identify and quantify mid-plane asymmetry in simulation images of galaxies that are within 3○ of edge-on orientation, allowing us to test whether the presence of a B/P-shaped bulge can be explained by a past buckling event. We apply our diagnostics to two nearly edge-on galaxies with B/P bulges from the Spitzer Survey of Stellar Structure in Galaxies, finding no mid-plane asymmetry, implying these galaxies formed their bulges either by resonant trapping or by buckling more than ∼5 Gyr ago. We conclude that the formation of B/P bulges through strong buckling may be a rare event in the past ∼5 Gyr

The dynamical state of bars in cluster dwarf galaxies: The cases of NGC 4483 and NGC 4516

Dwarf barred galaxies are the perfect candidates for hosting slowly-rotating bars. They are common in dense environments and they have a relatively shallow potential well, making them prone to heating by interactions. When an interaction induces bar formation, the bar should rotate slowly. They reside in massive and centrally-concentrated dark matter halos, which slow down the bar rotation through dynamical friction. While predictions suggest that slow bars should be common, measurements of bar pattern speed, using the Tremaine-Weinberg method, show that bars are mostly fast in the local Universe. We present a photometric and kinematic characterisation of bars hosted by two dwarf galaxies in the Virgo Cluster, NGC 4483 and NGC 4516. We derive the bar length and strength using the Next Generation Virgo Survey imaging and the circular velocity, bar pattern speed, and rotation rate using spectroscopy from the Multi Unit Spectroscopic Explorer. Including the previously studied galaxy IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in the dwarf galaxies are shorter and weaker, and rotate slightly slower with respect to those in massive galaxies. This could be due to a different bar formation mechanism and/or to a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine-Weinberg method to the galaxy low mass regime

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Direct measurement of the bar pattern speed in strongly and weakly barred galaxies

Bars are common in the local Universe across a wide range of galaxy morphologies, luminosities, and environments. The photometric, kinematic, and dynamical properties of bars depend on the formation and evolution process including the exchange of angular momentum with the other components. Their formation can be either induced by internal instabilities giving rise to a fast rotating bars slowing down with time, or by tidal interactions triggering slowly rotating bars. The measurement of the bar pattern speed allows to infer information about the mass distribution and the formation process of barred galaxies. In this thesis we aim at increasing the direct measurements of the bar pattern speed in strongly and weakly barred galaxies by applying the Tremaine-Weinberg method (TW) to integral-field spectroscopic data and at exploring the relations between the properties of bars and their host galaxies. We present a TW analysis of NGC4264, a barred lenticular galaxy in the region of the Virgo Cluster undergoing a tidal interaction with one neighbour. Analysing the surface photometry from SDSS i- and g-band images and the stellar kinematics from the integral-field spectroscopy performed with MUSE, we characterise the bar by measuring the radius, strength and pattern speed. We derive the circular velocity of the galaxy by correcting the stellar streaming velocity for asymmetric drift and calculate the bar rotation rate. NGC 4264 hosts a strong and large bar which is rotating fast. The measurement of the bar rotation rate allows us to infer that the formation of the bar of NGC4264 is due to internal processes and not triggered by the interaction. We investigate the formation process of weak bars. We select a sample of 29 nearby weakly barred galaxies, spanning a wide range of morphologies and luminosities. Combining our analysis with previous studies, we compare the properties of weak and strong bars. We measure the bar radius and strength from SDSS r-band images and bar pattern speed from the stellar kinematics obtained by CALIFA. 45 per cent of the visually-classified as weakly barred galaxies turn out not to host an actual bar component. The bar pattern speed is derived for 16 objects, including two ultrafast bars. With a quantitative criterion to differentiate weak and strong bars, we find that weakly barred galaxies host shorter bars and corotation radii than the strongly barred ones. Weak and strong bars have similar bar pattern speeds and rotation rates, which are all consistent with being fast. No difference is observed between the bulge prominence, whereas nearly all the weak bars reside in the disc inner parts, contrary to strong bars. We exclude that the bar weakening is only related to the bulge prominence and that the formation of weak bars is triggered by interactions. We suggest that weak bars may be evolved systems exchanging less angular momentum than strong bars. We revisit the relations between the properties of bars and their host galaxies. We collect 100 galaxies with a direct measurement of bar pattern speed. We consider the length, strength, pattern speed, corotation radius, and rotation rate of the bar as well as the Hubble type and absolute magnitude of the host galaxy. We also derive the bulge-to-total luminosity ratio for a subsample of galaxies. We limit our analysis to the 75 galaxies with a small relative error on the bar pattern speed and not hosting an ultrafast bar. We confirm earlier findings and we find that stronger bars rotate slower as predicted for the exchange of angular momentum during evolution. This result together with the fact that we observe stronger bars in bulge-dominated galaxies is in agreement with a scenario of downsizing in bar formation and co-evolution of bars and bulges if more massive galaxies formed earlier their bars and had sufficient time to slow down, grow in length, and in corotation. Finally, we discuss open issues and outline a few ideas for future investigations

DIRECT MEASUREMENT OF THE BAR PATTERN SPEED IN STRONGLY AND WEAKLY BARRED GALAXIES

Bars are common in the local Universe across a wide range of galaxy morphologies, luminosities, and environments. The photometric, kinematic, and dynamical properties of bars depend on the formation and evolution process including the exchange of angular momentum with the other components. Their formation can be either induced by internal instabilities giving rise to a fast rotating bars slowing down with time, or by tidal interactions triggering slowly rotating bars. The measurement of the bar pattern speed allows to infer information about the mass distribution and the formation process of barred galaxies. In this thesis we aim at increasing the direct measurements of the bar pattern speed in strongly and weakly barred galaxies by applying the Tremaine-Weinberg method (TW) to integral-field spectroscopic data and at exploring the relations between the properties of bars and their host galaxies. We present a TW analysis of NGC4264, a barred lenticular galaxy in the region of the Virgo Cluster undergoing a tidal interaction with one neighbour. Analysing the surface photometry from SDSS i- and g-band images and the stellar kinematics from the integral-field spectroscopy performed with MUSE, we characterise the bar by measuring the radius, strength and pattern speed. We derive the circular velocity of the galaxy by correcting the stellar streaming velocity for asymmetric drift and calculate the bar rotation rate. NGC 4264 hosts a strong and large bar which is rotating fast. The measurement of the bar rotation rate allows us to infer that the formation of the bar of NGC4264 is due to internal processes and not triggered by the interaction. We investigate the formation process of weak bars. We select a sample of 29 nearby weakly barred galaxies, spanning a wide range of morphologies and luminosities. Combining our analysis with previous studies, we compare the properties of weak and strong bars. We measure the bar radius and strength from SDSS r-band images and bar pattern speed from the stellar kinematics obtained by CALIFA. 45 per cent of the visually-classified as weakly barred galaxies turn out not to host an actual bar component. The bar pattern speed is derived for 16 objects, including two ultrafast bars. With a quantitative criterion to differentiate weak and strong bars, we find that weakly barred galaxies host shorter bars and corotation radii than the strongly barred ones. Weak and strong bars have similar bar pattern speeds and rotation rates, which are all consistent with being fast. No difference is observed between the bulge prominence, whereas nearly all the weak bars reside in the disc inner parts, contrary to strong bars. We exclude that the bar weakening is only related to the bulge prominence and that the formation of weak bars is triggered by interactions. We suggest that weak bars may be evolved systems exchanging less angular momentum than strong bars. We revisit the relations between the properties of bars and their host galaxies. We collect 100 galaxies with a direct measurement of bar pattern speed. We consider the length, strength, pattern speed, corotation radius, and rotation rate of the bar as well as the Hubble type and absolute magnitude of the host galaxy. We also derive the bulge-to-total luminosity ratio for a subsample of galaxies. We limit our analysis to the 75 galaxies with a small relative error on the bar pattern speed and not hosting an ultrafast bar. We confirm earlier findings and we find that stronger bars rotate slower as predicted for the exchange of angular momentum during evolution. This result together with the fact that we observe stronger bars in bulge-dominated galaxies is in agreement with a scenario of downsizing in bar formation and co-evolution of bars and bulges if more massive galaxies formed earlier their bars and had sufficient time to slow down, grow in length, and in corotation. Finally, we discuss open issues and outline a few ideas for future investigations