EIG - II. Intriguing characteristics of the most extremely isolated galaxies

Abstract

We have selected a sample of 41 extremely isolated galaxies (EIGs) from the local universe using both optical and HI ALFALFA redshifts (Spector & Brosch 2016). Narrow band H${}_{\alpha }$ and wide band imaging along with public data were used to derive star formation rates (SFRs), star formation histories (SFHs), and morphological classifications for the EIGs. We have found that the extreme isolation of the EIGs does not affect considerably their star-formation compared to field galaxies. EIGs are typically `blue cloud' galaxies that fit the `main sequence of star forming galaxies' and may show asymmetric star formation and strong compact star-forming regions. We discovered surprising environmental dependencies of the HI content, M${}_{HI}$, and of the morphological type of EIGs; The most isolated galaxies (of subsample EIG-1) have lower M${}_{HI}$ on average (with $2.5\sigma$ confidence) and a higher tendency to be early-types (with 0.94 confidence) compared to the less isolated galaxies of subsample EIG-2. To the best of our knowledge this is the first study that finds an effect in which an isolated sample shows a higher fraction of early-types compared to a less isolated sample. Both early-type and late-type EIGs follow the same colour-to-M${}_{\ast }$, SFR-to-M${}_{\ast }$ (`main sequence') and M${}_{HI}$-to-$M_{\ast }$ relations. This indicates that the mechanisms and factors governing star formation, colour and the M${}_{HI}$-to-M${}_{\ast }$ relation are similar in early-type and late-type EIGs, and that the morphological type of EIGs is not governed by their M${}_{HI}$ content, colour or SFR.

40 pages; 17 figures; 12 tables

References in corpus (22)

• Star Formation in AEGIS Field Galaxies since z=1.1 : The Dominance of Gradually Declining Star Formation, and the Main Sequence of Star-Forming Galaxies
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• UV Star Formation Rates in the Local Universe
• Galaxy Zoo: the dependence of morphology and colour on environment
• Spin alignment of dark matter haloes in filaments and walls
• The spin and orientation of dark matter halos within cosmic filaments
• The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region
• The origin of scatter in the stellar mass - halo mass relation of central galaxies in the EAGLE simulation
• Catalogues of isolated galaxies, isolated pairs, and isolated triplets in the local Universe
• Satellite abundances around bright isolated galaxies
• The Arecibo Legacy Fast ALFA Survey: IV. Strategies for Signal Identification and Survey Catalog Reliability
• The AMIGA sample of isolated galaxies. V. Quantification of the isolation
• The stellar-to-halo mass relations of local galaxies segregates by color
• The universal nature of subhalo accretion
• The Void Phenomenon Explained
• Where do "red and dead" early-type void galaxies come from?
• The HI Mass Function and Velocity Width Function of Void Galaxies in the Arecibo Legacy Fast ALFA Survey
• Catalog of Isolated Galaxies Selected from the 2MASS Survey
• Catalog of Nearby Isolated Galaxies in the Volume z<0.01
• Are (pseudo)bulges in isolated galaxies actually primordial relics?
• The stellar mass - halo mass relation from galaxy clustering in VUDS: a high star formation efficiency at z~3
• The NGC 672 and NGC 784 Galaxy Groups: Evidence for Galaxy Formation and Growth Along a Nearby Dark Matter Filament