Browsing by Author "Boardman, N."

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Are the Milky Way and Andromeda unusual? A comparison with Milky Way and Andromeda analogues
    (2020) Boardman, N.; Zasowski, G.; Newman, J. A.; Andrews, B.; Fielder, C.; Bershady, M.; Brinkmann, J.; Drory, N.; Krishnarao, D.; Lane, R. R.; Mackereth, T.; Masters, K.; Stringfellow, G. S.
    Our Milky Way provides a unique test case for galaxy evolution models because of our privileged position within the Milky Way's disc. This position also complicates comparisons between the Milky Way and external galaxies, due to our inability to observe the Milky Way from an external point of view. Milky Way analogue galaxies offer us a chance to bridge this divide by providing the external perspective that we otherwise lack. However, overprecise definitions of 'analogue' yield little-to-no galaxies, so it is vital to understand which selection criteria produce the most meaningful analogue samples. To address this, we compare the properties of complementary samples of Milky Way analogues selected using different criteria. We find the Milky Way to be within 1 sigma of its analogues in terms of star formation rate and bulge-to-total ratio in most cases, but we find larger offsets between the Milky Way and its analogues in terms of disc scale length; this suggests that scale length must be included in analogue selections in addition to other criteria if the most accurate analogues are to be selected. We also apply our methodology to the neighbouring Andromeda galaxy. We find analogues selected on the basis of strong morphological features to display much higher star formation rates than Andromeda, and we also find analogues selected on Andromeda's star formation rate to overpredict Andromeda's bulge extent. This suggests both structure and star formation rate should be considered when selecting the most stringent Andromeda analogues.
  • No Thumbnail Available
    Item
    Milky Way analogues in MaNGA: multiparameter homogeneity and comparison to the Milky Way
    (2020) Boardman, N.; Zasowski, G.; Seth, A.; Newman, J.; Andrews, B.; Bershady, M.; Bird, J.; Chiappini, C.; Fielder, C.; Fraser-McKelvie, A.; Jones, A.; Licquia, T.; Masters, K. L.; Minchev, I; Schiavon, R. P.; Brownstein, J. R.; Drory, N.; Lane, R. R.
    The Milky Way provides an ideal laboratory to test our understanding of galaxy evolution, owing to our ability to observe our Galaxy over fine scales. However, connecting the Galaxy to the wider galaxy population remains difficult, due to the challenges posed by our internal perspective and to the different observational techniques employed. Here, we present a sample of galaxies identified as Milky Way analogues on the basis of their stellar masses and bulge-to-total ratios, observed as part of the Mapping Nearby Galaxies at Apache Point Observatory survey. We analyse the galaxies in terms of their stellar kinematics and populations as well as their ionized gas contents. We find our sample to contain generally young stellar populations in their outskirts. However, we find a wide range of stellar ages in their central regions, and we detect central active galactic nucleus-like or composite-like activity in roughly half of the sample galaxies, with the other half consisting of galaxies with central star-forming emission or emission consistent with old stars. We measure gradients in gas metallicity and stellar metallicity that are generally flatter in physical units than those measured for the Milky Way; however, we find far better agreement with the Milky Way when scaling gradients by galaxies' disc scale lengths. From this, we argue much of the discrepancy in metallicity gradients to be due to the relative compactness of the Milky Way, with differences in observing perspective also likely to be a factor.