./toolbox
awv.pro
- Last modification date:
- Wed Sep 28 13:27:10 2016
Function to find the area, width, and velocity of a galaxy profile.
There are four ways in which the left and right (low channel number
and high channel number) edges of the galaxy profile can be determined. The
mode parameter selects one of these methods:
- 1 - As a fraction of the mean within the region of interest.
The mean of data from brange through erange is calculated. The
edges are then those locations where the data values are
greater than fract*mean for 3 consecutive channels starting
from the end points of the region of interest and searching
towards the center.
- 2 - As a fraction of the maximum value within the region of
interest. The peak of data from brange to erange is found.
The edges are then those locations where the data values
are greater than fract*(peak-rms) for 3 consecutive channels
starting from the end points of the region of interest and
searching towards the center.
- 3 - As a fraction of each of two peaks - identified by the
user. The user uses the cursor to mark two peaks in the
region of interest or those peaks are identified through
the lefthorn and righthorn parameters. The maximum value
within 10 channels of each user-supplied peak location is
found. The left edge is where the data value falls below
fract*(peak-rms) for 3 consecutive channels searched
from the location of the peak. The right-channel peak is
similarly used to find the right edge.
- 4 - A polynomial is fit to either side of the profile between
15-85% of (peak-rms) (where the peak is from the relevent side of
the profile - the two peaks are identified by the user). The velocity
of the polynomical fit at fract*(peak-rms) is then found for both sides
of the profile. The difference between the two is the width, the mean is
the central velocity. The order of the polynomial is chosen by the user
(linear fits are usually sufficient). This scheme (further described in
Springob etal 2006) has the advatange of averaging out noise effects from
either side of the profile.
In the first 3 modes, the final left and right edge are linear
interpolations to get the fractional channel where data value crossed
the threshold given by fract for that particular mode.
If an edge is not found, a warning is issued and the appropiate
end-point of the region of interest is used. Only the data values
within the region of interest are used here.
The returned value is a 6-element array with these values, in
this order.
- Area. The sum of data[i]*abs(vel[i+1]-vel[i-1])/2.0 for all i
from brange to erange (modes 1 and 2) or between the channels where
the data values first become negative moving out from the two peaks
found in mode 3 (not including that transition channel).
- Width. The absolute value of the difference between the left
and right edges as determined for that mode.
- Velocity. The mean of the left and right edges as determiend
for that mode.
- The 3 error estimates on the above values, in the same order.
The error on Area is only set for the fract=0.5 and fract=0.2 cases.
The Width and Velocity errors are only set by mode 4. For mode 4,
the Width error is always set at 2x the Velocity error. Unset error
estimates have a value of 0.0
Blanked data is ignored by this routine. Since the velocities
used to calculate widths and centers come from the centers of the
valid channels, ignoring the blanked data is equivalent to replacing
the blanked data by it's nearest non-blanked neighbor in the
direction of the edge searches. If the data is all blanked in the
region of interest, the returned values are all 0.
This code adapted from code in use at Arecibo. This particular
version was originally from Karen O'Neil.
Option 4 added by Karen Masters as part of work for GBT06A-027,
GBT06B-021, GBT06C-049,
GBT08B-003: "Mapping Mass in the Nearby Universe with 2MASS".
Contributed By: Karen O'Neil, Bob Garwood, and Karen Masters.
- Returns
-
the values in a 3 element array: [0] is the area, [1] is
the width and [2] is the velocity. Returns 0.0 for all 3 values on
error.
- Version
-
$Id$
| Parameters |
data
in, required
float array
|
The data values.
|
vel
in, required
float array
|
The velocities at each
data point, in km/s.
|
brange
in, required
integer
|
The first channel to use.
|
erange
in, required
integer
|
The last channel to use.
|
mode
in, required
integer
|
The method to use in
finding the returned values.
|
fract
in, required
float
|
Used in locating the edges of
the galaxy profile. See the documentation for more details.
|
| Keywords |
lefthorn
in, optional
float
|
The location (in
channels) of the left (low channel number) peak in the profile.
Used only in mode 3. If this or righthorn are not provided, the
user is asked to use the cursor to mark these locations.
|
righthorn
in, optional
float
|
The location (in
channels) of the right (high channel number) peak in the profile.
Used only in mode 3. If this or lefthorn are not provided, the user
is asked to use the cursor to mark these locations.
|
rms
in, optional
float
|
Used in modes 2 and 3 as
described above. If this is not supplied, defaults to the stddev of
data within the region of interest.
|
quiet
in, optional
boolean
|
When set, the results
are not printed to the terminal (they are still returned).
|
Produced by IDLdoc 1.6 on Wed Sep 28 13:27:37 2016