The Discovery of Seven Extremely Low Surface Brightness Galaxies in the Field of the Nearby Spiral Galaxy M101

Abstract

Dwarf satellite galaxies are a key probe of dark matter and of galaxy formation on small scales and of the dark matter halo masses of their central galaxies. They have very low surface brightness, which makes it difficult to identify and study them outside of the Local Group. We used a low surface brightness-optimized telescope, the Dragonfly Telephoto Array, to search for dwarf galaxies in the field of the massive spiral galaxy M101. We identify seven large, low surface brightness objects in this field, with effective radii of 10 − 30 arcseconds and central surface brightnesses of µ g ∼ 25.5 − 27.5 mag arcsec −2 . Given their large apparent sizes and low surface brightnesses, these objects would likely be missed by standard galaxy searches in deep fields. Assuming the galaxies are dwarf satellites of M101, their absolute magnitudes are in the range −11.6 M V −9.3 and their effective radii are 350 pc − 1.3 kpc. Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index (n ∼ 0.3 − 0.7). The properties of the sample are similar to those of well-studied dwarf galaxies in the Local Group, such as Sextans I and Phoenix. Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or background.

Discovery of Diffuse Dwarf Galaxy Candidates around M101

“…This corresponds to a rate of 1 dwarf candidate per ∼35 forwarded objects, which is comparable to or better than other semiautomated detection algorithms presented in the literature (e.g. Vollmer et al 2013;Merritt et al 2014;van der Burg et al 2016). False positives were mostly background galaxies and galaxy clusters (∼50%) or reflection halos around foreground stars (∼40%), which are especially prominent with CFHT-Megacam.…”

“…There have been many previous attempts to automate the detection of LSB galaxies, through algorithms or observational techniques, (e.g. Blanton et al 2011;Ferrarese et al 2012;Vollmer et al 2013;Merritt et al 2014;Duc et al 2015;van der Burg et al 2016;Greco et al 2017), and we present a detailed comparison with other recent efforts in §3.2.…”

H I observations of two new dwarf galaxies: Pisces A and B with the SKA Pathfinder KAT-7

“…While having some success recently for very nearby dwarfs in deep optical surveys, such as the Dark Energy Survey (Koposov et al 2015) and the PAN-STARRS 1 3π Survey (Laevens et al 2015), the task becomes very difficult as soon as one gets farther out in the Local Volume (5−10 Mpc). This was shown clearly with the discovery of seven dwarf galaxies close to M101, which have central surface brightnesses of µ g ∼ 25.5−27.5 mag arcsec −2 , well below the sky brightness, and was only possible through the development of a new instrument, the Dragonfly Telephoto Array (Merritt et al 2014).…”

Dwarf Galaxy Discoveries from the KMTNet Supernova Program. I. The NGC 2784 Galaxy Group*

“…The same group also reported ∼ 40 new dwarf galaxy candidates in the Centaurus group region (Müller et al 2017). Other studies have explored the NGC 5128 group (Crnojević et al 2016), the M 106 group (Kim et al 2011), the NGC 1023 group (Trentham & Tully 2009), and the M 101 group (Merritt et al 2014). These studies all discovered new dwarf galaxies, reaching as faint as M V ∼ −10 mag.…”