A global view on star formation: The GLOSTAR Galactic plane survey. II.
  Supernova Remnants in the first quadrant of the Milky Way
  Context. The properties of the population of Galactic supernova remnants
(SNRs) are essential to our understanding of the dynamics of the interstellar
medium (ISM) in the Milky Way. However, the completeness of the catalog of
Galactic SNRs is expected to be only ${\sim}30\%$, with on order 700 SNRs yet
to be detected. Deep interferometric radio continuum surveys of the Galactic
plane help in rectifying this apparent deficiency by identifying low surface
brightness SNRs and compact SNRs that have not been detected in previous
surveys. However, SNRs are routinely confused with H II regions, which can have
similar radio morphologies. Radio spectral index, polarization, and emission at
mid-infrared (MIR) wavelengths can help distinguish between SNRs and H II
regions. Aims. We aim to identify SNR candidates using continuum images from
the Karl G. Jansky Very Large Array GLObal view of the STAR formation in the
Milky Way (GLOSTAR) survey. Methods. GLOSTAR is a C-band (4--8 GHz) radio
wavelength survey of the Galactic plane covering $358^{\circ} \leq l \leq
60^{\circ}, |b| \leq 1^{\circ}$. The continuum images from this survey, which
resulted from observations with the most compact configuration of the array,
have an angular resolution of $18''$. We searched for SNRs in these images to
identify known SNRs, previously identified SNR candidates, and new SNR
candidates. We study these objects in MIR surveys and the GLOSTAR polarization
data to classify their emission as thermal or nonthermal. Results. We identify
157 SNR candidates, of which 80 are new. Polarization measurements provide
evidence of nonthermal emission from 9 of these candidates. We find that two
previously identified candidates are filaments. We also detect emission from 91
of the 94 known SNRs in the survey region. Four of these are reclassified as H
II regions following detection in MIR surveys. (Abridged)
