We present mid-infrared photometry and measured global properties of the 100 largest galaxies in the sky, including the well-studied Magellanic Clouds, Local Group galaxies M31 and M33, the Fornax and Virgo Galaxy Cluster giants, and many of the most spectacular Messier objects (e.g., M51 and M83). This is the first release of a larger catalog of extended sources as imaged in the mid-infrared, called the WISE Extended Source Catalogue (WXSC).
Corresponding author: Thomas Jarrett; firstname.lastname@example.org
M31 - Andromeda
M33 - Triangulum
In this study, we measure their global attributes, including integrated flux, surface brightness and radial distribution. The largest of the large are the LMC, SMC and the Andromeda Galaxy, which are also the brightest mid-infrared galaxies in the sky. We interrogate the large galaxies using WISE colors, which serve as proxies for four general types of galaxies: bulge-dominated spheroidals, intermediate semi-quiescent disks, star-forming spirals, and AGN-dominated. The colors reveal a tight "sequence" that spans 5 magnitudes in (W2 - W3) color, ranging from early to late-types, and low to high star-forming activity; we fit the functional form given by:
Departures from this sequence may reveal nuclear, starburst, and merging events. Physical properties and luminosity attributes are computed, notably the diameter, aggregate stellar mass and the dust-obscured star formation activity. To effectively study and compare these galaxy characteristics, we introduce the "pinwheel" diagram which depicts physical properties with respect to the median value observed for WISE galaxies in the local universe. Utilized with the WXSC, this diagram will delineate between different kinds of galaxies, identifying those with similar star formation and structural properties. Finally, we present the mid-infrared photometry of the 25 brightest globular clusters in the sky, for which many are also the largest and brightest objects orbiting the Milky Way, including Omega Centauri, 47 Tucanae and a number of famed night-sky targets (e.g., M13).
We have constructed a whole-sky atlas of (chiefly) nearby, bright galaxies and globular clusters called the WISE
Extended Source Catalogue (WXSC). For each source, we have constructed new deep and wide mosaics from which to measure and characterize the target galaxy, as well as sources that are nearby in projected radial distance. To date, we have measured over 70,000 sources. For the first release, we choose the largest angular galaxies in the sky, starting from the Magellanic Clouds, to the major Local Group galaxies such as M31 and M33, to nearby galaxy groups and clusters (Virgo and Fornax). The WXSC will allow us to compare the most well-studied galaxies with large and more distant galaxies samples from WISE
, and the SKA pathfinders.
To view the details and images of the 100 galaxies examined in WXSC, click here
or go to the tab above.
We have measured the global and internal radial brightness properties of the 100 largest galaxies based on the WISE W1 (3.4 μm) 1 - σsky isophotal radius (about 23 mag arcsec-2), which typically reaches axi-symmetric-averaged depths of 25 mag arcsec-2 or approximately 28 mag arcsec-2 in the AB system. We present the results for angular diameters, integrated flux from isophotes and “total” extractions from both asymptotic apertures and fitting to the radial profile to levels below the noise, surface brightness, and colors, (W1-W2) and (W2-W3). The Magellanic Clouds, M31, and M33 are large enough that special methods were required to extract their light from the intervening foreground Galactic emission.
Because of the high quality measurements from the largest and brightest galaxies in the sky (WXSC), the WISE color-color diagram reveals a tight sequence that represents galaxy morphology and star-formation history, including present-day activity. We use the rest-frame-corrected measurements from the largest and highest S/N galaxies to fit the functional form of this WISE color-color “sequence”, given by:
Offsets from the sequence arise from the usual photometric scatter, and more meaningfully, from excess infrared emission associated with nuclear activity from AGN and starbursts.
The sample is sub-divided by the WISE colors, which serve as proxies for four general types of galaxies: bulge-dominated spheroidals, intermediate semi-quiescent disk, SF spirals, and AGN-dominated systems. Physical properties and attributes are computed based on their distance, notably the diameter, aggregate stellar mass and the dust-obscured star formation rate. We use this classification scheme to study their global properties: effective surface brightness, size, bulge-to-disk ratios, luminosity. We compare the half-light radii and surface brightnesses between WISE W1 (3.4 μm) and 2MASS (2.2 μm) measurements, showing that W1 radii are much larger and surface brightnesses much fainter than those extracted from the less sensitive 2MASS imaging, notably for dwarf and low-surface brightness galaxies.
We find that the global properties are not remarkable compared to galaxies in the local universe, except in the sense that we can detect and discern the smallest and lowest-mass dwarf and satellite galaxies because of their close proximity. Nevertheless, the 100 largest galaxies include bright cluster (Virgo and Fornax) galaxies (which have enormous diameters, > 100 kpc, very high B/T ratios, and aggregate stellar masses; NGC1316 is the most massive), starbursts (such as NGC253 and M82 with SFRs ten times the rate of the Milky Way), and AGN (e.g. Circinus and NGC1068, with surface brightnesses that are so bright that they image-saturate in the mid-IR).
In terms of the star formation history, the 100 largest galaxies tend to have lower specific-SFRs compared to field galaxies, notably compared to a much larger sample of nearby galaxies belonging to the WXSC and compared to deeper redshift-selected samples, such as those from GAMA G12 (Jarrett+2017).
The low mass end is dominated by dwarf spheroids (e.g., NGC 0185), which have very low SFRs and hence, slowly building their bulge population. Early-type disk galaxies, such as M81, are passively building with rates that fall below the sequence trend. Late-type spirals, such as M 83, are actively building with rates perfectly consistent with the SFH sequence observed in the GAMA G12 study.
To efficiently display the attributes that we are capable of estimating with WISE measurements, we introduce a “pinwheel” diagram that depicts the physical properties with respect to the median value observed for galaxies in the WXSC. These six attributes are the physical diameter, surface brightness, colors, SFR and stellar mass. We show that with this diagram, it is possible to delineate between different kinds of galaxies, identifying those with similar SFHs, for example. The Pinwheel Diagrams will be a featured product as part of the WXSC image, catalog and ancillary data archive.
Finally, we present the 25 brightest globular clusters in the sky, for which many are also the largest and brightest objects outside of the Milky Way. Most notably Omega Centauri, 47 Tucanae and a number of famed night-sky targets (e.g., Hercules /M13). GCs have mid-IR color properties that are similar to spheroidal galaxies, indeed Omega Centauri is essentially this type of object, indicative of their dominant evolved-stellar populations.
Highlighted Figures (see Jarrett et al 2019 for details):
The machine-readable tables from Jarrett et al. 2019 can be accessed here
The machine-readable tables from Jarrett et al. 2019 can be accessed here