ASTRO: NGC 672 and IC 1727

NGC 672/UGC 1256 (north left of center) and IC 1727/UGC 1249 are an
interesting, nearby, pair of galaxies in Triangulum. The red-shift
distances are highly unreliable saying they are only 7 and 3 million
light-years away respectively. This can't be true. Other distance
measurements at NED put the distance to NGC 674 in the range of 23 to 32
million light-years and that of IC 1724 between 21 and 23 million
light-years. Adam Block while at NOAO put the distance to both at 18
million light-years which is the distance cited in the paper quoted
below though it gives 15 million light-years for IC 1727. Most sources
consider them as interacting so the true distance to both should be
close to the same. Radio measurements show the HI clouds around these
two galaxies to be contiguous, not just overlapping. I found this
interesting note at NED:

"UGC 1256 In this SB(s)cd spiral companion of UGC 1249, the HII regions
are arranged along a bar in the inner parts and seem to draw a weak
spiral structure around it. For this late type galaxy, no clear nucleus
can be seen on the continuum map which shows several knots in the
central part. The rotation curve, like that of its neighbor UGC 1249, is
irregular, notably in the inner parts where it shows a counter-rotation
motion. Indeed, one can see an inversion of the sign of the velocities
within 20 arcsec of the center, corresponding to two HII regions (that
surrounded by the isovelocity 420 and that on its right), with a
symmetric behaviour for both sides of the rotation curve. The center of
rotation has been chosen in order to have the two sides of the rotation
curve symmetrical, but we want to underline the fact that this peculiar
motion of counter-rotation persists if we choose another knot as the
center, showing that this motion is real. The curve begins to be fairly
symmetric beyond 100 arcsec (3.9 kpc), seeming to reach a plateau around
80 km s^-1^. However, according to the HI data, the plateau could be
around 120 km s^-1^. Unlike what Carozzi-Meysonnier (1982) claimed
(namely that UGC 1256 was less affected by the interaction according to
optical studies), it is hard to estimate which galaxy is the more
perturbed. Concerning its content in atomic hydrogen, the WHISP data
show that its column density is very high in the optical disk (more than
20 x 10^20^ atoms cm^-2^), and that there is an extension of neutral gas
to the north of the galaxy, which could be a tidal tail due to the
interaction."

For IC 1727 it says:
"This SB(s)m galaxy exhibits an asymmetric structure on the DSS image
also observed on the Ha emission, which is mainly localized in what
looks like a central bar and on the north-west side, suggesting a
distorted spiral arm. No clear nucleus was detected on the continuum map
and the center of rotation was chosen in order to derive the most
regular and symmetric rotation curve possible. This rotation curve is
quite chaotic but it seems that (from the approaching side) we reach a
plateau at 70 km s-1 beyond 130 arcsec (2.8 kpc). About 9 arcmin to the
north-east, UGC 1249 has a companion, UGC 1256, with which it seems to
be interacting. Indeed, on the HI map derived by WHISP, one can see that
their HI disks are contiguous and their velocity fields are regular and
show a continuity in the isovelocity lines. The amplitude of the HI
velocity field is in agreement with that derived by GHASP, confirming
that we reach a plateau on the approaching side. "
http://adsabs.harvard.edu/cgi-bin/bi...6A...399...51G

Only three other galaxies in the frame have red shift data and one of
those is nearly off the frame. The pair of galaxies along the north
edge toward the left corner are CGCG 482-017 at about 480 million
light-years. The remaining galaxy is also at 480 million light-years.
It is very small and faint. For those who want to track it down it is
at pixel 123x954 near the left edge below center. The only "bright"
galaxy in the image besides NGC 672 and IC 1727 is LEDA 1803573. It is
the orange spindle just east (left) of the south end of IC 1727. NED
had no redshift data for it. It is obviously a background galaxy.

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Rick
--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

Rick,

nice picture of this duo/trio/group of galaxies. I only have a black and
white version with less detail...

Stefan

"Rick Johnson" schrieb im Newsbeitrag
.com...
NGC 672/UGC 1256 (north left of center) and IC 1727/UGC 1249 are an
interesting, nearby, pair of galaxies in Triangulum. The red-shift
distances are highly unreliable saying they are only 7 and 3 million
light-years away respectively. This can't be true. Other distance
measurements at NED put the distance to NGC 674 in the range of 23 to 32
million light-years and that of IC 1724 between 21 and 23 million
light-years. Adam Block while at NOAO put the distance to both at 18
million light-years which is the distance cited in the paper quoted
below though it gives 15 million light-years for IC 1727. Most sources
consider them as interacting so the true distance to both should be
close to the same. Radio measurements show the HI clouds around these
two galaxies to be contiguous, not just overlapping. I found this
interesting note at NED:

"UGC 1256 In this SB(s)cd spiral companion of UGC 1249, the HII regions
are arranged along a bar in the inner parts and seem to draw a weak
spiral structure around it. For this late type galaxy, no clear nucleus
can be seen on the continuum map which shows several knots in the
central part. The rotation curve, like that of its neighbor UGC 1249, is
irregular, notably in the inner parts where it shows a counter-rotation
motion. Indeed, one can see an inversion of the sign of the velocities
within 20 arcsec of the center, corresponding to two HII regions (that
surrounded by the isovelocity 420 and that on its right), with a
symmetric behaviour for both sides of the rotation curve. The center of
rotation has been chosen in order to have the two sides of the rotation
curve symmetrical, but we want to underline the fact that this peculiar
motion of counter-rotation persists if we choose another knot as the
center, showing that this motion is real. The curve begins to be fairly
symmetric beyond 100 arcsec (3.9 kpc), seeming to reach a plateau around
80 km s^-1^. However, according to the HI data, the plateau could be
around 120 km s^-1^. Unlike what Carozzi-Meysonnier (1982) claimed
(namely that UGC 1256 was less affected by the interaction according to
optical studies), it is hard to estimate which galaxy is the more
perturbed. Concerning its content in atomic hydrogen, the WHISP data
show that its column density is very high in the optical disk (more than
20 x 10^20^ atoms cm^-2^), and that there is an extension of neutral gas
to the north of the galaxy, which could be a tidal tail due to the
interaction."

For IC 1727 it says:
"This SB(s)m galaxy exhibits an asymmetric structure on the DSS image
also observed on the Ha emission, which is mainly localized in what
looks like a central bar and on the north-west side, suggesting a
distorted spiral arm. No clear nucleus was detected on the continuum map
and the center of rotation was chosen in order to derive the most
regular and symmetric rotation curve possible. This rotation curve is
quite chaotic but it seems that (from the approaching side) we reach a
plateau at 70 km s-1 beyond 130 arcsec (2.8 kpc). About 9 arcmin to the
north-east, UGC 1249 has a companion, UGC 1256, with which it seems to
be interacting. Indeed, on the HI map derived by WHISP, one can see that
their HI disks are contiguous and their velocity fields are regular and
show a continuity in the isovelocity lines. The amplitude of the HI
velocity field is in agreement with that derived by GHASP, confirming
that we reach a plateau on the approaching side. "
http://adsabs.harvard.edu/cgi-bin/bi...6A...399...51G

Only three other galaxies in the frame have red shift data and one of
those is nearly off the frame. The pair of galaxies along the north
edge toward the left corner are CGCG 482-017 at about 480 million
light-years. The remaining galaxy is also at 480 million light-years.
It is very small and faint. For those who want to track it down it is
at pixel 123x954 near the left edge below center. The only "bright"
galaxy in the image besides NGC 672 and IC 1727 is LEDA 1803573. It is
the orange spindle just east (left) of the south end of IC 1727. NED
had no redshift data for it. It is obviously a background galaxy.

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Rick
--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".