Abstract
Abstract We report deep, single-dish 21 cm observations of NGC 1052-DF2, taken with the Green Bank Telescope. NGC 1052-DF2, proposed to be lacking in dark matter, is currently classified as an ultra-diffuse galaxy in the NGC 1052 group. We do not detect the galaxy, and derive an upper limit on the H i mass. The galaxy is extremely gas poor, and we find that a detection at a distance of 19 Mpc and using a line width of 3.2 km s−1 would have an upper limit of M ⊙. At this mass limit, the gas fraction of neutral gas mass to stellar mass is extremely low, at M H i /M ⋆ < 0.0027. This extremely low gas fraction, comparable to Galactic dwarf spheroidals and gas-poor dwarf ellipticals, implies that either the galaxy is within the virial radius of NGC 1052, where its gas has been stripped due to its proximity to the central galaxy, or that NGC 1052-DF2 is at a distance that is large enough to inhibit detection of its gas. We also estimate the upper limit of the H i mass of NGC 1052-DF2 resided at 13 Mpc. This would give an H i mass of M ⊙, and an H i gas fraction if M H i /M ⋆ < 0.0024, becoming even more extreme for its environment. While the dark matter fraction would be less extreme at this distance, the neutral gas fraction would be unprecedented for an object in a low-density environment.
Highlights
The extremely low surface brightness galaxy NGC 1052–DF2 was discovered by Karachentsev et al (2000), who labeled it a dwarf galaxy candidate. van Dokkum et al (2018b) measured the total mass of the galaxy by measuring the radial velocities of ten luminous globular clusters
The gas fraction of neutral gas mass to stellar mass is extremely low, at MHi/M < 0.0027. This extremely low gas fraction, comparable to Galactic dwarf spheroidals and gas-poor dwarf ellipticals, implies that either the galaxy is within the virial radius of NGC 1052, where its gas has been stripped due to its proximity to the central galaxy, or that NGC 1052–DF2 is at distance large enough to inhibit detection of its gas
Trujillo et al (2018) proposed that many of the unusual features of NGC 1052–DF2 may be explained if the galaxy, which van Dokkum et al (2018b) estimates a distance of 19 Mpc, was brought to a distance of 13 Mpc, making it a typical low surface brightness galaxy without the anomalies described by van Dokkum et al (2018b). van Dokkum et al (2018a) address this distance concern by analyzing the color-magnitude diagram (CMD) of NGC 1052–DF2 and arrive at a distance consistent with the 19 Mpc estimate
Summary
The extremely low surface brightness galaxy NGC 1052–DF2 was discovered by Karachentsev et al (2000), who labeled it a dwarf galaxy candidate. van Dokkum et al (2018b) measured the total mass of the galaxy by measuring the radial velocities of ten luminous globular clusters. Comparing the estimated total mass with the derived stellar mass of the galaxy, which van Dokkum et al (2018b) determined to be M ≈ 2 × 108 M , they obtain a Mhalo/M of order one They propose that the galaxy is deficient in dark matter. Laporte et al (2018) suggested a lack of robustness in the method used by van Dokkum et al. Trujillo et al (2018) proposed that many of the unusual features of NGC 1052–DF2 may be explained if the galaxy, which van Dokkum et al (2018b) estimates a distance of 19 Mpc, was brought to a distance of 13 Mpc, making it a typical low surface brightness galaxy without the anomalies described by van Dokkum et al (2018b).
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