A SPECTROSCOPIC STUDY OF THE GIANT LOW SURFACE BRIGHTNESS GALAXY MALIN 1

International audienceLow Surface Brightness galaxies (LSBs) represent a significant fraction of galaxies in the nearby universe. However, despite their large fraction, the structure and origin of this class of galaxies is still poorly understood, especially due to the lack of high-resolution kinematics and spectroscopy. Malin 1 is the largest known low surface brightness galaxy to date, the archetype of so-called giant LSBs. We present new results based on spectroscopic observations of Malin 1, using the Hα and [OII]3727 emission lines in order to bring new constraints on the internal dynamics of this galaxy. We have extracted a total of 16 spectra from different regions of Malin 1 and calculated the inner rotational velocities using the observed shift in the emission line wavelengths. We show for the first time a steep rise in the rotation curve of Malin 1 up to ∼400 km s −1 (within r < 10 kpc), which had not been observed in any of the previous works on this galaxy. We will discuss the implications of this result in comparison with existing works on Malin 1 and also the possibility for making a new mass model for this galaxy

Pola nafkah petani kopi: kajian petani kopi di desa tertinggal di Kabupaten Jeneponto

Kemiskinan sangat identik dengan masyarakat petani, jeratan kemiskinan seolah menjadi penyakit masyarakat yang sudah turun temurun. Salah satu faktor yang memperparah kondisi ini adalah kurangnya sumber daya masyarakat petani dalam mengelola potensi yang dimiliki.Penelitian ini bertujuan untuk melihat pola nafkah petani kopi di sebuah desa tertinggal. Penelitian ini melibatkan 70 keluarga petani yang diwawancarai. Analisis data menggunakan pendekatan data kuantitatif yang kemudian didukung dengan pendekatan kualitatif. Hasil penelitian menunjukkan bahwa, ketidakmampuan petani dalam memenuhi kebutuhannya sepenuhnya bukan karena kurangnya pendapatan petani namun, ketidakmampuan petani dalam mengelola keuangan dalam rangka memenuhi kebutuhan keluarga. Pendapatan petani yang tidak merata sepanjang tahun dimana petani hanya akan mendapatkan pendatan lebih di masa musim panen kopi dan hortikultura yaitu pada bulan April, Mei dan Juli, selebihnya petani hanya menggantungkan pendapatannya pada tanaman hortikultura jangka pendek dan sektor lain diluar pertanian seperti buruh bangunan di kota, berdagang, supir dan lain-lain. Sehingga secara umum masyarakat petani akan nampak miskin akibat ketidakmampuannya dalam memenuhi kebutuhannya. Oleh karena itu, untuk dapat mengelola kebutuhan diperlukan adanya peningkatan sumberdaya petani dalam mengelola pendapatan sehingga mampu merencanakan pemenuhan kebutuhan keluarga dalam satu tahun

The slippery slope of dust attenuation curves: Correlation of dust attenuation laws with star-to-dust compactness up to z = 4

Aims. We investigate dust attenuation of 122 heavily dust-obscured galaxies detected with the Atacama Large Millimeter Array (ALMA) and Herschel in the COSMOS field. We search for correlations between dust attenuation recipes and the variation of physical parameters, mainly the effective radii of galaxies, their star formation rates (SFR), and stellar masses, and aim to understand which of the commonly used laws best describes dust attenuation in dusty star-forming galaxies at high redshift. Methods. We make use of the extensive photometric coverage of the COSMOS data combined with highly-resolved dust continuum maps from ALMA. We use CIGALE to estimate various physical properties of these dusty objects, mainly their SFR, their stellar masses and their attenuation. We infer galaxy effective radii (Re) using GALFIT in the Y band of HSC and ALMA continuum maps. We use these radii to investigate the relative compactness of the dust continuum and the extension of the rest-frame UV/optical Re(y)/Re(ALMA). Results. We find that the physical parameters calculated from our models strongly depend on the assumption of dust attenuation curve. As expected, the most impacted parameter is the stellar mass, which leads to a change in the "starburstiness" of the objects. We find that taking into account the relative compactness of star-to-dust emission prior to SED fitting is crucial, especially when studying dust attenuation of dusty star-forming galaxies. Shallower attenuation curves did not show a clear preference of compactness with attenuation, while the Calzetti attenuation curve preferred comparable spatial extent of unattenuated stellar light and dust emission. The evolution of the Re(UV)/Re(ALMA) ratio with redshift peeks around the cosmic noon in our sample of DSFGs, showing that this compactness is correlated with the cosmic SFR density of these dusty sources.Comment: 18 pages, 13 figures, accepted for publication in A&A. Abstract abridged for arXiv submissio

Star-formation driven outflows in local dwarf galaxies as revealed from [CII] observations by Herschel

We characterize the physical properties of star-formation driven outflows in a sample of 29 local dwarf galaxies drawn from the Dwarf Galaxy Survey. We make use of Herschel/PACS archival data to search for atomic outflow signatures in the wings of individual [CII] 158 um spectra and in their stacked line profile. We find a clear excess of emission in the high-velocity tails of 11 sources which can be explained with an additional broad component in the modeling of their spectra. The remaining objects are likely hosts of weaker outflows that can still be detected in the average stacked spectrum. In both cases, we estimate the atomic mass outflow rates which result to be comparable with the star-formation rates of the galaxies, implying mass-loading factors of the order of unity. Outflow velocities in all the 11 galaxies with individual detection are larger than (or compatible with) the escape velocities of their dark matter halos, with an average fraction of 40% of gas escaping into the intergalactic medium (IGM). Depletion timescales due to outflows are lower than those due to gas consumption by star formation in most of our sources, ranging from hundred million to a few billion years. Our outflows are mostly consistent with momentum-driven winds generated by the radiation pressure of young stellar populations on dust grains, although the energy-driven scenario is not excluded if considering a coupling efficiency up to 20% between the energy injected by supernova (SN) and the interstellar medium. Our results suggest that galactic outflows can regulate the star formation history of dwarf galaxies as they are able to enrich with metals the circumgalactic medium of these sources, bringing on average a non-negligible amount of gas into the IGM. Our findings are suitable for tuning chemical evolution models attempting to describe the physical processes shaping the evolution of dwarf galaxies.Comment: Accepted for publication in A&

MUSE observations of the giant low surface brightness galaxy Malin 1: Numerous HII regions, star formation rate, metallicity, and dust attenuation

Giant low-surface brightness (GLSB) galaxies are an extreme class of objects with very faint and extended gas-rich disks. Malin 1 is the largest GLSB galaxy known to date, but its formation is still poorly understood. We use VLT/MUSE IFU spectroscopic observations of Malin 1 to reveal, for the first time, the presence of H$\alpha$ emission distributed across numerous regions along its disk, up to radial distances of $\sim$100 kpc. We made an estimate of the dust attenuation using the Balmer decrement and found that Malin 1 has a mean H$\alpha$ attenuation of 0.36 mag. We observe a steep decline in the star formation rate surface density ($\Sigma_{\rm SFR}$) within the inner 20 kpc, followed by a shallow decline in the extended disk. Similarly, the gas phase metallicity we estimated shows a steep gradient in the inner 20 kpc, followed by a flattening of the metallicity in the extended disk with a relatively high value of $\sim$0.6 $Z_{\odot}$. We found that the normalized abundance gradient of the inner disk is similar to values found in normal galaxies but with an extreme value in the extended disk. A comparison of the star formation rate surface density and gas surface density shows that, unlike normal disk galaxies or other LSBs, Malin 1 exhibits a very low star formation efficiency. Owing to the detection of emission lines over a large part of the disk of Malin 1, this work sheds light on the star formation processes in this unique galaxy, highlighting its extended star-forming disk, dust attenuation, almost flat metallicity distribution in the outer disk, and exceptionally low star-formation efficiency. Our findings contribute to a more detailed understanding of the formation of the giant disk of Malin 1 and also constrain possible proposed scenarios on the nature of GLSB galaxies in general.Comment: 12 pages, 9 figures, accepted for publication in A&

Decoding the IRX-\beta\ dust attenuation relation in star-forming galaxies at intermediate redshift

We aim to understand what drives the IRX-\beta dust attenuation relation at intermediate redshift (0.5 < z < 0.8) in star-forming galaxies. We investigate the role of various galaxy properties in shaping this observed relation. We use robust [O ii] {\lambda}3727, [O iii] {\lambda}{\lambda}4959, 5007, and H\beta line detections of our statistical sample of 1049 galaxies to estimate the gas-phase metallicities. We derive key physical properties that are necessary to study galaxy evolution, such as the stellar masses and the star formation rates, using the spectral energy distribution fitting tool CIGALE. Equivalently, we study the effect of galaxy morphology (mainly the S\'ersic index n and galaxy inclination) on the observed IRX-\beta scatter. We also investigate the role of the environment in shaping dust attenuation in our sample. We find a strong correlation of the IRX-\beta relation on gas-phase metallicity in our sample, and also strong correlation with galaxy compactness characterized by the S\'ersic indexes. Correlations are also seen with stellar masses, specific star formation rates and the stellar ages of our sources. Metallicity strongly correlates with the IRX-\beta scatter, this also results from the older stars and higher masses at higher beta values. Galaxies with higher metallicities show higher IRX and higher beta values. The correlation with specific dust mass strongly shifts the galaxies away from the IRX-\beta relation towards lower \b{eta} values. We find that more compact galaxies witness a larger amount of attenuation than less compact galaxies. There is a subtle variation in the dust attenuation scatter between edge-on and face-on galaxies, but the difference is not statistically significant. Galaxy environments do not significantly affect dust attenuation in our sample of star-forming galaxies at intermediate redshift.Comment: 14 pages, 13 figures, accepted for publication in A&

Variation of optical and infrared properties of galaxies with their surface brightness

Although low surface brightness galaxies (LSBs) contribute a large fraction to the number density of galaxies, their properties are still poorly known. LSBs are often considered dust poor, based only on a few studies. We use, for the first time, a large sample of LSBs and high surface brightness galaxies (HSBs) with deep observational data to study their dust properties as a function of surface brightness. Our sample consists of 1631 optically selected galaxies at $z < 0.1$ from the North Ecliptic Pole (NEP) wide field. We use the large set of data available in this field, from UV to FIR. We measured the optical size and the surface brightness of the targets, and analyzed their spectral energy distribution using the CIGALE fitting code. We found that the specific star formation rate and specific infrared luminosity (total infrared luminosity per stellar mass) remain mostly flat as a function of surface brightness for both LSBs and HSBs that are star-forming but decline steeply for the quiescent galaxies. The majority of LSBs in our sample have negligible dust attenuation (A$_{V} < 0.1$ mag), except for about 4% of them that show significant attenuation with a mean A$_{V}$ of 0.8 mag. We found that these LSBs also have a high $\textit{r}$-band mass-to-light ratio ($M/L_r>3$ M$_{\odot}$/L$_{\odot}$), and show similarity to the extreme giant LSBs from the literature, indicating a possibly higher dust attenuation in giant LSBs as well. This work provides a large catalog of LSBs and HSBs with detailed measurements of their several optical and infrared physical properties. Our results suggest that the dust content of LSBs is more varied than previously thought, with some of them having significant attenuation making them fainter than their intrinsic value. This will have serious implications for the observation and analysis of LSBs with current/upcoming surveys like JWST and LSST.Comment: 16 pages, 12 figures, accepted for publication in A&

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XIII. The role of ram-pressure stripping in transforming the diffuse and ultra-diffuse galaxies in the Virgo cluster

Low-surface-brightness galaxies (LSBs) contribute to a significant fraction of all the galaxies in the Universe. Ultra-diffuse galaxies (UDGs) form a subclass of LSBs that has attracted a lot of attention in recent years (although its definition may vary between studies). Although UDGs are found in large numbers in galaxy clusters, groups, and in the field, their formation and evolution are still very much debated. Using a comprehensive set of multiwavelength data from the NGVS (optical), VESTIGE (H$\alpha$ narrowband), and GUViCS (UV) surveys, we studied a sample of 64 diffuse galaxies and UDGs in the Virgo cluster to investigate their formation history. We analyzed the photometric colors and surface-brightness profiles of these galaxies and then compared them to models of galaxy evolution, including ram-pressure stripping (RPS) events to infer any possible strong interactions with the hot cluster gas in the past. While our sample consists mainly of red LSBs, which is typical in cluster environments, we found evidence of a color variation with the cluster-centric distance. Blue, HI-bearing, star-forming diffuse galaxies are found at larger distances from the cluster center than the rest of the sample. The comparison of our models with multifrequency observations suggests that most of the galaxies of the sample might have undergone a strong RPS event in their lifetime, on average 1.6 Gyr ago (with a large dispersion, and RPS still ongoing for some of them). This process resulted in the transformation of initially gas-rich diffuse blue galaxies into gas-poor and red ones that form the dominant population now, the more extreme UDGs having undergone the process in a more distant past on average. The RPS in dense environments could be one of the major mechanisms for the formation of the large number of quiescent UDGs we observe in galaxy clusters.Comment: 57 pages, 14 Figures, accepted for publication in A&