The GALEX/S4G UV-IR color-color diagram: catching Spiral Galaxies away from the Blue Sequence.

Figure caption: Left : (FUV − NUV) versus (NUV − [3.6]) color-color diagram. Morphological types are represented by color (see legend). We define the blue and red sequence by dividing the plot into two regions and fitting a least-squares 1-D polynomial (a
Figure caption: Left : (FUV − NUV) versus (NUV − [3.6]) color-color diagram. Morphological types are represented by color (see legend). We define the blue and red sequence by dividing the plot into two regions and fitting a least-squares 1-D polynomial (a
Advertised on
References
2015, ApJ, 800, L19

We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6 µm photometry for >2000 galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue Sequence (GBS)" in the (FUV − NUV) versus (NUV − [3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale (τ ) and a degeneracy between τ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying starforming galaxies and objects that are just evolving to (or from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS, at (NUV − [3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by M_[3.6]), since both massive (M_* > 10^11 M_solar) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sa's and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on timescale of 10^8 years.

This research was performed in the context of the DAGAL project (dagalnetwork.eu), funded by an ITN grant from the EU.

1 Departamento de Astrofísica y CC. de la Atmósfera, Universidad Complutense de Madrid, E-28040 Madrid, Spain
2 Aix Marseille Université, CNGRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille, France
3 I.N.A.F., Osservatorio Astronomico di Bologna, via Ranzani 1 I-40127 Bologna, Italy
4 European Southern Observatory, Casilla 19001, Santiago 19, Chile
5 National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903, USA
6 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
7 Astronomy Division, Department of Physics, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland
8 Kapteyn Astronomical Institute, Postbus 800, NL-9700 AV Groningen, The Netherlands
9 Instituto de Astrofísica de Canarias, Vía Láctea, S/N, E-38205 La Laguna, Spain
10 Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain

News type
Research news

It may interest you

  • Research news
    Scientific results with the QUIJOTE-MFI wide survey: The anomalous microwave emission in our Galaxy and M31
    In the 90s, the COBE satellite discovered that not all the microwave emission from our Galaxy behaved as expected. Part of this signal was later assigned to a fresh new emission component, spatially correlated with the Galactic dust emission, which showed greater importance in the microwave range of frequencies. It has been named since as “anomalous microwave emission”, or AME. The current main hypothesis to explain the AME origin is that it is emitted by small dust particles which undergo fast spinning movements. In Fernández-Torreiro et al. (2023), we study the observational properties of
    Advertised on
  • Hertzsprung–Russel diagram blue supergiants
    Research news
    Challenging the theoretically predicted mass-loss rate increase of blue supergiants in the bi-stability region of the stellar winds
    The properties of blue supergiants are key for constraining the end of the main sequence phase, a phase during which massive stars spend most of their lifetimes. The lack of fast-rotating stars below 21.000K, a temperature around which stellar winds change in behaviour, has been proposed to be caused by enhanced mass-loss rates, which would spin down the star. Alternatively, the lack of fast-rotating stars may be the result of stars reaching the end of the main sequence. Here, we combine newly derived estimates of photospheric and wind parameters, wind terminal velocities from the literature
    Advertised on
  • Planetary Nebula M57
    Research news
    Hydrogenated amorphous carbon grains as a carrier of unidentified IR bands in planetary nebulae
    It is well known that fullerenes – big, complex, and highly resistant carbon molecules with potential applications in nanotechnology – are mostly seen in planetary nebulae (PNe); old dying stars with progenitor masses similar to our Sun. Fullerenes, like C60 and C70, have been detected in PNe whose infrared (IR) spectra are dominated by broad unidentified IR (UIR) plateau emissions. The identification of the chemical species (structure and composition) responsible for such UIR emission widely present in the Universe is a mystery in astrochemistry; although they are believed to be carbon-rich
    Advertised on